├── .gitignore ├── LICENSE ├── README.md ├── behavioral ├── chain_of_responsibility │ ├── README.md │ └── main.go ├── command │ ├── README.md │ └── main.go ├── interpreter │ ├── README.md │ └── main.go ├── iterator │ ├── README.md │ └── main.go ├── mediator │ ├── README.md │ └── main.go ├── memento │ ├── README.md │ └── main.go ├── observer │ ├── README.md │ └── main.go ├── state │ ├── README.md │ └── main.go ├── strategy │ ├── README.md │ └── main.go ├── template │ ├── README.md │ └── main.go └── visitor │ ├── README.md │ └── main.go ├── creational ├── abstract_factory │ ├── README.md │ └── main.go ├── builder │ ├── README.md │ └── main.go ├── factory │ ├── README.md │ ├── log.txt │ └── main.go ├── prototype │ ├── README.md │ └── main.go └── singleton │ ├── README.md │ └── main.go ├── go.mod ├── go.sum ├── other ├── data_access_object │ ├── README.md │ └── main.go ├── dependency_injection │ ├── README.md │ ├── article.txt │ └── main.go ├── repository │ ├── README.md │ └── main.go └── service_locator │ ├── README.md │ └── main.go └── structural ├── adapter ├── README.md └── main.go ├── bridge ├── README.md └── main.go ├── composite ├── README.md └── main.go ├── decorator ├── README.md └── main.go ├── facade ├── README.md └── main.go ├── flyweight ├── README.md └── main.go └── proxy ├── README.md └── main.go /.gitignore: -------------------------------------------------------------------------------- 1 | # If you prefer the allow list template instead of the deny list, see community template: 2 | # https://github.com/github/gitignore/blob/main/community/Golang/Go.AllowList.gitignore 3 | # 4 | # Binaries for programs and plugins 5 | *.exe 6 | *.exe~ 7 | *.dll 8 | *.so 9 | *.dylib 10 | 11 | # Test binary, built with `go test -c` 12 | *.test 13 | 14 | # Output of the go coverage tool, specifically when used with LiteIDE 15 | *.out 16 | 17 | # Dependency directories (remove the comment below to include it) 18 | # vendor/ 19 | 20 | # Go workspace file 21 | go.work 22 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. 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Limitation of Liability. 601 | 602 | IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING 603 | WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS 604 | THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY 605 | GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE 606 | USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF 607 | DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD 608 | PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), 609 | EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF 610 | SUCH DAMAGES. 611 | 612 | 17. Interpretation of Sections 15 and 16. 613 | 614 | If the disclaimer of warranty and limitation of liability provided 615 | above cannot be given local legal effect according to their terms, 616 | reviewing courts shall apply local law that most closely approximates 617 | an absolute waiver of all civil liability in connection with the 618 | Program, unless a warranty or assumption of liability accompanies a 619 | copy of the Program in return for a fee. 620 | 621 | END OF TERMS AND CONDITIONS 622 | 623 | How to Apply These Terms to Your New Programs 624 | 625 | If you develop a new program, and you want it to be of the greatest 626 | possible use to the public, the best way to achieve this is to make it 627 | free software which everyone can redistribute and change under these terms. 628 | 629 | To do so, attach the following notices to the program. It is safest 630 | to attach them to the start of each source file to most effectively 631 | state the exclusion of warranty; and each file should have at least 632 | the "copyright" line and a pointer to where the full notice is found. 633 | 634 | 635 | Copyright (C) 636 | 637 | This program is free software: you can redistribute it and/or modify 638 | it under the terms of the GNU General Public License as published by 639 | the Free Software Foundation, either version 3 of the License, or 640 | (at your option) any later version. 641 | 642 | This program is distributed in the hope that it will be useful, 643 | but WITHOUT ANY WARRANTY; without even the implied warranty of 644 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 645 | GNU General Public License for more details. 646 | 647 | You should have received a copy of the GNU General Public License 648 | along with this program. If not, see . 649 | 650 | Also add information on how to contact you by electronic and paper mail. 651 | 652 | If the program does terminal interaction, make it output a short 653 | notice like this when it starts in an interactive mode: 654 | 655 | Copyright (C) 656 | This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 657 | This is free software, and you are welcome to redistribute it 658 | under certain conditions; type `show c' for details. 659 | 660 | The hypothetical commands `show w' and `show c' should show the appropriate 661 | parts of the General Public License. Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # design-patterns-in-go 2 | 3 | A list of design patterns implemented in Go with REAL WORLD examples! 4 | 5 | ## "Gang of Four" patterns 6 | 7 | ### Creational Patterns 8 | 9 | - **Singleton**: Ensures a class only has one instance and provides a global point of access to it. 10 | - **Factory**: Provides an interface for creating objects in a super class, but allows subclasses to alter the type of objects that will be created. 11 | - **Abstract Factory**: Provides an interface for creating families of related or dependent objects without specifying their concrete classes. 12 | - **Builder**: Separates the construction of a complex object from its representation so that the same construction process can create different representations. 13 | - **Prototype**: Specifies the kind of objects to create using a prototypical instance and create new objects by copying this prototype. 14 | 15 | ### Structural Patterns 16 | 17 | - **Adapter**: Converts the interface of a class into another interface the clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces. 18 | - **Decorator**: Attaches additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality. 19 | - **Facade**: Provides a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use. 20 | - **Composite**: Composes objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly. 21 | - **Proxy**: Provides a surrogate or placeholder for another object to control access to it. 22 | - **Bridge**: Decouples an abstraction from its implementation so that the two can vary independently. 23 | - **Flyweight**: Uses sharing to support large numbers of fine-grained objects efficiently. 24 | 25 | ### Behavioral Patterns 26 | 27 | - **Observer**: Defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. 28 | - **Command**: Encapsulates a request as an object, thereby letting you parameterize clients with queues, requests, and operations. 29 | - **Strategy**: Defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from the clients that use it. 30 | - **State**: Allows an object to alter its behavior when its internal state changes. The object will appear to change its class. 31 | - **Template**: Defines the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure. 32 | - **Iterator**: Provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation. 33 | - **Mediator**: Defines an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently. 34 | - **Memento**: Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later. 35 | - **Chain of Responsability**: Used to achieve loose coupling in software design where a request from the client is passed to a chain of objects to process them. 36 | - **Interpreter**: Defines a grammatical representation for a language and provides an interpreter to deal with this grammar. 37 | - **Visitor**: Used when we have to perform an operation on a group of similar kind of Objects. 38 | 39 | ## Other Patterns 40 | 41 | - **Active Record Pattern**: Found in many modern ORM (Object Relational Mapping) libraries, the Active Record pattern ties database access directly to an object, where the object mirrors the database table. Each instance of the object corresponds to a row in the table. 42 | - **Repository Pattern**: Acts as a kind of in-memory domain object collection. Client objects construct query specifications declaratively and submit them to Repository for satisfaction. 43 | - **Data Access Object (DAO) Pattern**: Provides an abstract interface to a database or a persistent storage mechanism. 44 | - **Dependency Injection (DI) Pattern**: A way to achieve Inversion of Control (IoC) in a system by breaking dependencies between higher-level and lower-level software layers. 45 | - **Model-View-ViewModel (MVVM) Pattern**: Primarily used for designing the user interface. It divides an application into three interconnected components: Model (represents the data), View (represents the UI), and ViewModel (acts as a bridge that handles the data presentation in the View). 46 | - **CQRS (Command Query Responsibility Segregation)**: A pattern where you separate the command (write) operations from the query (read) operations, ensuring that a method is either a command that performs an action or a query that returns data, but not both. 47 | - **Event Sourcing**: Capturing all changes to an application state as a sequence of events, allowing for replaying these events to restore the application's state. 48 | - **Flux/Redux Pattern**: Used mainly in frontend frameworks like React. It involves a unidirectional data flow where the view sends actions to a central dispatcher, which updates the store, and the changed state then reflects in the view. 49 | - **Saga Pattern**: A mechanism to manage long-running, complex processes or workflows. Sagas manage failures, maintain consistency, and coordinate activities. 50 | - **Service Locator Pattern**: Provides a centralized point from which objects can retrieve services (like dependency injection but involves the client requesting its dependencies). 51 | - **Null Object Pattern**: A design pattern that uses polymorphism to represent the absence of an object by providing an alternative that offers default do-nothing behavior. 52 | - **Value Object Pattern**: Small objects that represent a descriptive aspect of the domain with no conceptual identity. They are immutable, meaning that they cannot be altered once they are created. 53 | - **Thread Pool Pattern**: Allows a limited set of threads to be reused for executing multiple tasks. 54 | -------------------------------------------------------------------------------- /behavioral/chain_of_responsibility/README.md: -------------------------------------------------------------------------------- 1 | # Chain of Responsibility 2 | 3 | The Chain of Responsibility design pattern is a behavioral pattern that allows you to pass a request along a chain of handlers. Each handler decides either to process the request or to pass it along the chain. This pattern allows you to decouple the sender and receiver components, making the code more modular and easier to maintain. 4 | 5 | In the Chain of Responsibility pattern, usually, each handler has a reference to the next handler in the chain. A handler decides whether it can handle the request; if it can, it does so, otherwise, it delegates the request to the next handler in the chain. 6 | 7 | ### Participants in the Chain of Responsibility Pattern 8 | 9 | - **Handler**: The interface that declares the method for handling requests. 10 | - **ConcreteHandler**: The class that implements the Handler interface and performs the actual work, or delegates the work to the next handler in the chain. 11 | - **Client**: The class that initiates the request to a handler on the chain. 12 | 13 | ## Example 14 | 15 | Let's consider a simple example where we have different levels of logging: `Info`, `Warning`, and `Error`. Each logging level is handled by a different logger. However, if one logger can't handle a particular log level, it passes the request to the next logger in the chain. 16 | 17 | Here is how you can implement this in Go: 18 | 19 | ```go 20 | // Log levels 21 | const ( 22 | Info = iota 23 | Warning 24 | Error 25 | ) 26 | 27 | // Handler interface 28 | type Logger interface { 29 | SetNext(Logger) 30 | LogMessage(int, string) 31 | } 32 | 33 | // ConcreteHandler 34 | type ConsoleLogger struct { 35 | level int 36 | next Logger 37 | } 38 | 39 | func (c *ConsoleLogger) SetNext(next Logger) { 40 | c.next = next 41 | } 42 | 43 | func (c *ConsoleLogger) LogMessage(level int, message string) { 44 | if c.level <= level { 45 | fmt.Printf("Writing to console: %s\n", message) 46 | } 47 | if c.next != nil { 48 | c.next.LogMessage(level, message) 49 | } 50 | } 51 | 52 | // Another ConcreteHandler 53 | type ErrorLogger struct { 54 | level int 55 | next Logger 56 | } 57 | 58 | func (e *ErrorLogger) SetNext(next Logger) { 59 | e.next = next 60 | } 61 | 62 | func (e *ErrorLogger) LogMessage(level int, message string) { 63 | if e.level <= level { 64 | fmt.Printf("Writing to error log: %s\n", message) 65 | } 66 | if e.next != nil { 67 | e.next.LogMessage(level, message) 68 | } 69 | } 70 | 71 | func main() { 72 | // Setting up the chain 73 | consoleLogger := &ConsoleLogger{level: Info} 74 | errorLogger := &ErrorLogger{level: Error} 75 | 76 | consoleLogger.SetNext(errorLogger) 77 | 78 | // Making requests 79 | consoleLogger.LogMessage(Info, "This is an informational message.") 80 | consoleLogger.LogMessage(Error, "This is an error message.") 81 | } 82 | ``` 83 | 84 | In this example: 85 | 86 | - `Logger` is the `Handler` interface that defines the method for logging messages. 87 | - `ConsoleLogger` and `ErrorLogger` are `ConcreteHandlers`. Each decides whether it can handle the given logging level or pass it to the next handler in the chain. 88 | - The `main()` function acts as the `Client` that initiates the requests. 89 | 90 | Run the code, and you'll see that depending on the log level, the appropriate logger(s) handle the message. 91 | 92 | With the Chain of Responsibility pattern, you can easily add more loggers in the chain without modifying the existing code, thus following the Open/Closed Principle. 93 | -------------------------------------------------------------------------------- /behavioral/chain_of_responsibility/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | // Log levels 6 | const ( 7 | Info = iota 8 | Warning 9 | Error 10 | ) 11 | 12 | // Handler interface 13 | type Logger interface { 14 | SetNext(Logger) 15 | LogMessage(int, string) 16 | } 17 | 18 | // ConcreteHandler 19 | type ConsoleLogger struct { 20 | level int 21 | next Logger 22 | } 23 | 24 | func (c *ConsoleLogger) SetNext(next Logger) { 25 | c.next = next 26 | } 27 | 28 | func (c *ConsoleLogger) LogMessage(level int, message string) { 29 | if c.level <= level { 30 | fmt.Printf("Writing to console: %s\n", message) 31 | } 32 | if c.next != nil { 33 | c.next.LogMessage(level, message) 34 | } 35 | } 36 | 37 | // Another ConcreteHandler 38 | type ErrorLogger struct { 39 | level int 40 | next Logger 41 | } 42 | 43 | func (e *ErrorLogger) SetNext(next Logger) { 44 | e.next = next 45 | } 46 | 47 | func (e *ErrorLogger) LogMessage(level int, message string) { 48 | if e.level <= level { 49 | fmt.Printf("Writing to error log: %s\n", message) 50 | } 51 | if e.next != nil { 52 | e.next.LogMessage(level, message) 53 | } 54 | } 55 | 56 | func main() { 57 | // Setting up the chain 58 | consoleLogger := &ConsoleLogger{level: Info} 59 | errorLogger := &ErrorLogger{level: Error} 60 | 61 | consoleLogger.SetNext(errorLogger) 62 | 63 | // Making requests 64 | consoleLogger.LogMessage(Info, "This is an informational message.") 65 | consoleLogger.LogMessage(Error, "This is an error message.") 66 | } 67 | -------------------------------------------------------------------------------- /behavioral/command/README.md: -------------------------------------------------------------------------------- 1 | # Command 2 | 3 | The command design pattern is a behavioral design pattern used to encapsulate a request as an object, thereby allowing for parameterization of clients with queues, requests, and operations. It also allows for the decoupling of the sender and receiver objects. The Command Pattern consists of the following main components: 4 | 5 | - Command: This defines an interface for executing an operation. 6 | - ConcreteCommand: This is a subclass of Command and implements the execute method by invoking the corresponding operation on the receiver object. 7 | - Client: The Client creates a ConcreteCommand object and sets its receiver. 8 | - Invoker: It asks the command to carry out the request. 9 | - Receiver: It knows how to perform the operation to satisfy a request. 10 | 11 | The command pattern can be particularly useful when you need to allow for undo functionality, queuing of commands, task scheduling or logging of command operations. It also provides greater flexibility in terms of organizing code and adding new commands without modifying existing code. 12 | 13 | ## Example 14 | 15 | Here's a practical example that could be part of a text editor, where we implement a simple undo functionality using the command pattern in Go. 16 | 17 | ```go 18 | // Command interface 19 | type Command interface { 20 | Execute() 21 | Unexecute() 22 | } 23 | 24 | // Receiver 25 | type TextEditor struct { 26 | text string 27 | } 28 | 29 | func (t *TextEditor) Add(s string) { 30 | t.text += s 31 | } 32 | 33 | func (t *TextEditor) Delete(n int) { 34 | if n <= len(t.text) { 35 | t.text = t.text[:len(t.text)-n] 36 | } 37 | } 38 | 39 | func (t *TextEditor) Display() { 40 | fmt.Println(t.text) 41 | } 42 | 43 | // ConcreteCommand for Adding Text 44 | type AddTextCommand struct { 45 | editor *TextEditor 46 | text string 47 | } 48 | 49 | func (c *AddTextCommand) Execute() { 50 | c.editor.Add(c.text) 51 | } 52 | 53 | func (c *AddTextCommand) Unexecute() { 54 | c.editor.Delete(len(c.text)) 55 | } 56 | 57 | // Invoker 58 | type CommandInvoker struct { 59 | history []Command 60 | } 61 | 62 | func (i *CommandInvoker) Execute(c Command) { 63 | c.Execute() 64 | i.history = append(i.history, c) 65 | } 66 | 67 | func (i *CommandInvoker) Undo() { 68 | if len(i.history) > 0 { 69 | lastCommand := i.history[len(i.history)-1] 70 | lastCommand.Unexecute() 71 | i.history = i.history[:len(i.history)-1] 72 | } 73 | } 74 | ``` 75 | 76 | In this example, the text editor is our receiver, and we have a specific command for adding text (`AddTextCommand`) with both Execute and `Unexecute` methods. The invoker (`CommandInvoker`) manages the execution of commands and keeps a history of executed commands, allowing for simple undo functionality. 77 | 78 | By employing the command pattern, we've made it easy to extend the text editor with additional commands (like copy, paste, formatting) without changing existing code. The undo functionality is also neatly encapsulated within the invoker, allowing for more advanced features like multi-level undo or redo with minimal changes. 79 | -------------------------------------------------------------------------------- /behavioral/command/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | // Command interface 6 | type Command interface { 7 | Execute() 8 | Unexecute() 9 | } 10 | 11 | // Receiver 12 | type TextEditor struct { 13 | text string 14 | } 15 | 16 | func (t *TextEditor) Add(s string) { 17 | t.text += s 18 | } 19 | 20 | func (t *TextEditor) Delete(n int) { 21 | if n <= len(t.text) { 22 | t.text = t.text[:len(t.text)-n] 23 | } 24 | } 25 | 26 | func (t *TextEditor) Display() { 27 | fmt.Println(t.text) 28 | } 29 | 30 | // ConcreteCommand for Adding Text 31 | type AddTextCommand struct { 32 | editor *TextEditor 33 | text string 34 | } 35 | 36 | func (c *AddTextCommand) Execute() { 37 | c.editor.Add(c.text) 38 | } 39 | 40 | func (c *AddTextCommand) Unexecute() { 41 | c.editor.Delete(len(c.text)) 42 | } 43 | 44 | // Invoker 45 | type CommandInvoker struct { 46 | history []Command 47 | } 48 | 49 | func (i *CommandInvoker) Execute(c Command) { 50 | c.Execute() 51 | i.history = append(i.history, c) 52 | } 53 | 54 | func (i *CommandInvoker) Undo() { 55 | if len(i.history) > 0 { 56 | lastCommand := i.history[len(i.history)-1] 57 | lastCommand.Unexecute() 58 | i.history = i.history[:len(i.history)-1] 59 | } 60 | } 61 | 62 | func main() { 63 | editor := &TextEditor{} 64 | invoker := &CommandInvoker{} 65 | 66 | addCommand1 := &AddTextCommand{editor: editor, text: "Hello, "} 67 | invoker.Execute(addCommand1) 68 | editor.Display() // Output: Hello, 69 | 70 | addCommand2 := &AddTextCommand{editor: editor, text: "world!"} 71 | invoker.Execute(addCommand2) 72 | editor.Display() // Output: Hello, world! 73 | 74 | invoker.Undo() 75 | editor.Display() // Output: Hello, 76 | } 77 | -------------------------------------------------------------------------------- /behavioral/interpreter/README.md: -------------------------------------------------------------------------------- 1 | # Interpreter 2 | 3 | The Interpreter design pattern is a behavioral design pattern that provides a way to evaluate language grammar for particular languages. It involves defining a representation for the language's grammar and an interpreter to interpret the grammar. The pattern is particularly useful for building compilers and interpreters, but it's generally less commonly used than other design patterns. 4 | 5 | ### Participants 6 | 7 | - **Abstract Expression**: Declares an abstract Interpret operation that is common to all nodes in the abstract syntax tree. 8 | - **Terminal Expression**: Implements the Interpret operation for terminal expressions. 9 | - **Nonterminal Expression**: Implements the Interpret operation for grammar rules which include other expressions. 10 | - **Context**: Contains the global information that is interpreted. 11 | 12 | ## Example 13 | 14 | Let's consider a simple arithmetic problem where we want to evaluate an expression given in Reverse Polish Notation (RPN). In RPN, every operator follows all of its operands. For example, the expression `3 4 +` evaluates to `7`. 15 | 16 | Here is how you can implement it in Go: 17 | 18 | ```go 19 | // Expression interface 20 | type Expression interface { 21 | Interpret() int 22 | } 23 | 24 | // TerminalExpression 25 | type Number struct { 26 | value int 27 | } 28 | 29 | func (n *Number) Interpret() int { 30 | return n.value 31 | } 32 | 33 | // NonTerminalExpression 34 | type Operation struct { 35 | left, right Expression 36 | operator string 37 | } 38 | 39 | func (o *Operation) Interpret() int { 40 | switch o.operator { 41 | case "+": 42 | return o.left.Interpret() + o.right.Interpret() 43 | case "-": 44 | return o.left.Interpret() - o.right.Interpret() 45 | case "*": 46 | return o.left.Interpret() * o.right.Interpret() 47 | case "/": 48 | return o.left.Interpret() / o.right.Interpret() 49 | } 50 | return 0 51 | } 52 | 53 | // Context 54 | type Context struct { 55 | stack []Expression 56 | } 57 | 58 | func (c *Context) Parse(tokens []string) Expression { 59 | for _, token := range tokens { 60 | if token == "+" || token == "-" || token == "*" || token == "/" { 61 | right := c.stack[len(c.stack)-1] 62 | c.stack = c.stack[:len(c.stack)-1] 63 | left := c.stack[len(c.stack)-1] 64 | c.stack = c.stack[:len(c.stack)-1] 65 | 66 | c.stack = append(c.stack, &Operation{ 67 | left: left, 68 | right: right, 69 | operator: token, 70 | }) 71 | } else { 72 | num, _ := strconv.Atoi(token) 73 | c.stack = append(c.stack, &Number{value: num}) 74 | } 75 | } 76 | return c.stack[len(c.stack)-1] 77 | } 78 | ``` 79 | 80 | In this example: 81 | 82 | - `Expression` is the Abstract Expression that declares an `Interpret()` method. 83 | - `Number` is a Terminal Expression that represents individual numbers. 84 | - `Operation` is a Non-terminal Expression that represents arithmetic operations. 85 | - `Context` stores the global information (in this case, the operand stack), and it also has a `Parse` method to build the abstract syntax tree for the given RPN expression. 86 | 87 | 88 | The Interpreter pattern lets you build a parse tree from your language of choice and then evaluate it. However, it's worth noting that this pattern can lead to a large number of classes and can be hard to manage for complex grammars. In such cases, alternative techniques such as parser combinators or parser generators may be more appropriate. 89 | -------------------------------------------------------------------------------- /behavioral/interpreter/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | "strconv" 6 | "strings" 7 | ) 8 | 9 | // Expression interface 10 | type Expression interface { 11 | Interpret() int 12 | } 13 | 14 | // TerminalExpression 15 | type Number struct { 16 | value int 17 | } 18 | 19 | func (n *Number) Interpret() int { 20 | return n.value 21 | } 22 | 23 | // NonTerminalExpression 24 | type Operation struct { 25 | left, right Expression 26 | operator string 27 | } 28 | 29 | func (o *Operation) Interpret() int { 30 | switch o.operator { 31 | case "+": 32 | return o.left.Interpret() + o.right.Interpret() 33 | case "-": 34 | return o.left.Interpret() - o.right.Interpret() 35 | case "*": 36 | return o.left.Interpret() * o.right.Interpret() 37 | case "/": 38 | return o.left.Interpret() / o.right.Interpret() 39 | } 40 | return 0 41 | } 42 | 43 | // Context 44 | type Context struct { 45 | stack []Expression 46 | } 47 | 48 | func (c *Context) Parse(tokens []string) Expression { 49 | for _, token := range tokens { 50 | if token == "+" || token == "-" || token == "*" || token == "/" { 51 | right := c.stack[len(c.stack)-1] 52 | c.stack = c.stack[:len(c.stack)-1] 53 | left := c.stack[len(c.stack)-1] 54 | c.stack = c.stack[:len(c.stack)-1] 55 | 56 | c.stack = append(c.stack, &Operation{ 57 | left: left, 58 | right: right, 59 | operator: token, 60 | }) 61 | } else { 62 | num, _ := strconv.Atoi(token) 63 | c.stack = append(c.stack, &Number{value: num}) 64 | } 65 | } 66 | return c.stack[len(c.stack)-1] 67 | } 68 | 69 | func main() { 70 | context := &Context{} 71 | expression := context.Parse(strings.Fields("3 4 + 2 * 7 /")) 72 | 73 | fmt.Println("Result:", expression.Interpret()) 74 | } 75 | -------------------------------------------------------------------------------- /behavioral/iterator/README.md: -------------------------------------------------------------------------------- 1 | # Iterator 2 | 3 | The "Iterator" design pattern provides a way to access the elements of an aggregate object (like a collection) sequentially without exposing its underlying representation. The main purpose of this pattern is to decouple the iteration logic from the collection itself. 4 | 5 | The Iterator pattern typically involves at least three components: 6 | 7 | - Iterator: This defines an interface for accessing and traversing elements. 8 | - ConcreteIterator: This implements the Iterator interface, keeping track of the current position in the traversal of the aggregate. 9 | - Aggregate: This defines an interface for creating an Iterator object. 10 | - ConcreteAggregate: This implements the Aggregate interface and returns an instance of the ConcreteIterator. 11 | 12 | ## Example 13 | 14 | Iterators are often used in real-world software systems to abstract the process of iterating over different types of collections. For a more practical example, let's consider a scenario where we have a software system managing different types of data sources. One common task might be to iterate over records from each data source, regardless of how that data is stored or represented. 15 | 16 | **Scenario**: Let's say you're building a system that manages user profiles. The profiles can be stored in different data structures: a slice (array-like structure in Go) and a map. You want to have a consistent way to iterate over user profiles, irrespective of the underlying data structure. 17 | 18 | **Implementation**: 19 | 20 | 1. **UserProfile**: Represents the user profile. 21 | 2. **Aggregate**: An interface to create an Iterator. 22 | 3. **Iterator**: Interface to traverse through elements. 23 | 24 | **Concrete Aggregates**: 25 | 1. **UserProfileSlice**: Represents a slice of user profiles. 26 | 2. **UserProfileMap**: Represents a map of user profiles. 27 | 28 | **Concrete Iterators**: 29 | 1. **SliceIterator**: Iterates over a slice. 30 | 2. **MapIterator**: Iterates over a map. 31 | 32 | Here's how you can implement the above: 33 | 34 | ```go 35 | type UserProfile struct { 36 | ID int 37 | Name string 38 | } 39 | 40 | // Aggregate interface 41 | type UserProfileCollection interface { 42 | CreateIterator() Iterator 43 | } 44 | 45 | // Iterator interface 46 | type Iterator interface { 47 | HasNext() bool 48 | Next() *UserProfile 49 | } 50 | 51 | // Concrete Aggregate: Slice 52 | type UserProfileSlice struct { 53 | profiles []UserProfile 54 | } 55 | 56 | func (us *UserProfileSlice) CreateIterator() Iterator { 57 | return &SliceIterator{profiles: us.profiles, index: 0} 58 | } 59 | 60 | type SliceIterator struct { 61 | profiles []UserProfile 62 | index int 63 | } 64 | 65 | func (si *SliceIterator) HasNext() bool { 66 | return si.index < len(si.profiles) 67 | } 68 | 69 | func (si *SliceIterator) Next() *UserProfile { 70 | if si.HasNext() { 71 | profile := &si.profiles[si.index] 72 | si.index++ 73 | return profile 74 | } 75 | return nil 76 | } 77 | 78 | // Concrete Aggregate: Map 79 | type UserProfileMap struct { 80 | profiles map[int]UserProfile 81 | keys []int 82 | } 83 | 84 | func (um *UserProfileMap) CreateIterator() Iterator { 85 | keys := make([]int, 0, len(um.profiles)) 86 | for k := range um.profiles { 87 | keys = append(keys, k) 88 | } 89 | return &MapIterator{profiles: um.profiles, keys: keys, index: 0} 90 | } 91 | 92 | type MapIterator struct { 93 | profiles map[int]UserProfile 94 | keys []int 95 | index int 96 | } 97 | 98 | func (mi *MapIterator) HasNext() bool { 99 | return mi.index < len(mi.keys) 100 | } 101 | 102 | func (mi *MapIterator) Next() *UserProfile { 103 | if mi.HasNext() { 104 | key := mi.keys[mi.index] 105 | profile := mi.profiles[key] 106 | mi.index++ 107 | return &profile 108 | } 109 | return nil 110 | } 111 | ``` 112 | 113 | The main advantage here is that the code iterating over user profiles remains the same, irrespective of whether the underlying data structure is a slice or a map. This decouples the iteration logic from the data structure, making the code more modular and easier to maintain. 114 | -------------------------------------------------------------------------------- /behavioral/iterator/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | type UserProfile struct { 6 | ID int 7 | Name string 8 | } 9 | 10 | // Aggregate interface 11 | type UserProfileCollection interface { 12 | CreateIterator() Iterator 13 | } 14 | 15 | // Iterator interface 16 | type Iterator interface { 17 | HasNext() bool 18 | Next() *UserProfile 19 | } 20 | 21 | // Concrete Aggregate: Slice 22 | type UserProfileSlice struct { 23 | profiles []UserProfile 24 | } 25 | 26 | func (us *UserProfileSlice) CreateIterator() Iterator { 27 | return &SliceIterator{profiles: us.profiles, index: 0} 28 | } 29 | 30 | type SliceIterator struct { 31 | profiles []UserProfile 32 | index int 33 | } 34 | 35 | func (si *SliceIterator) HasNext() bool { 36 | return si.index < len(si.profiles) 37 | } 38 | 39 | func (si *SliceIterator) Next() *UserProfile { 40 | if si.HasNext() { 41 | profile := &si.profiles[si.index] 42 | si.index++ 43 | return profile 44 | } 45 | return nil 46 | } 47 | 48 | // Concrete Aggregate: Map 49 | type UserProfileMap struct { 50 | profiles map[int]UserProfile 51 | keys []int 52 | } 53 | 54 | func (um *UserProfileMap) CreateIterator() Iterator { 55 | keys := make([]int, 0, len(um.profiles)) 56 | for k := range um.profiles { 57 | keys = append(keys, k) 58 | } 59 | return &MapIterator{profiles: um.profiles, keys: keys, index: 0} 60 | } 61 | 62 | type MapIterator struct { 63 | profiles map[int]UserProfile 64 | keys []int 65 | index int 66 | } 67 | 68 | func (mi *MapIterator) HasNext() bool { 69 | return mi.index < len(mi.keys) 70 | } 71 | 72 | func (mi *MapIterator) Next() *UserProfile { 73 | if mi.HasNext() { 74 | key := mi.keys[mi.index] 75 | profile := mi.profiles[key] 76 | mi.index++ 77 | return &profile 78 | } 79 | return nil 80 | } 81 | 82 | func main() { 83 | sliceData := &UserProfileSlice{ 84 | profiles: []UserProfile{ 85 | {ID: 1, Name: "Alice"}, 86 | {ID: 2, Name: "Bob"}, 87 | }, 88 | } 89 | 90 | mapData := &UserProfileMap{ 91 | profiles: map[int]UserProfile{ 92 | 3: {ID: 3, Name: "Charlie"}, 93 | 4: {ID: 4, Name: "Dave"}, 94 | }, 95 | } 96 | 97 | // Iterating over slice 98 | iterator := sliceData.CreateIterator() 99 | fmt.Println("Iterating over slice:") 100 | for iterator.HasNext() { 101 | fmt.Println(iterator.Next()) 102 | } 103 | 104 | // Iterating over map 105 | iterator = mapData.CreateIterator() 106 | fmt.Println("\nIterating over map:") 107 | for iterator.HasNext() { 108 | fmt.Println(iterator.Next()) 109 | } 110 | } 111 | -------------------------------------------------------------------------------- /behavioral/mediator/README.md: -------------------------------------------------------------------------------- 1 | # Mediator 2 | 3 | The Mediator design pattern is a behavioral design pattern that aims to reduce coupling between classes that communicate with each other. Instead of classes communicating directly with each other, they interact through a mediator object. This makes it easier to modify, add, or remove components without having to alter the other interacting components. The Mediator pattern is particularly useful in large and complex systems where you want to control the interactions between classes. 4 | 5 | ## Participants in the Mediator Pattern 6 | 7 | - **Mediator**: The interface that declares methods to communicate with Colleagues. 8 | - **ConcreteMediator**: Implements the Mediator interface and keeps track of all Colleagues. 9 | - **Colleague**: An interface for components that will communicate with each other via the Mediator. 10 | - **ConcreteColleague**: The class that will implement the Colleague interface and communicate via the Mediator. 11 | 12 | ## Example 13 | 14 | Let's consider a chat room as an example, where multiple users can send messages to the chat room, and the chat room will display the messages to all users. 15 | 16 | Here is a simple implementation in Go: 17 | 18 | ```go 19 | // Mediator interface 20 | type Mediator interface { 21 | SendMessage(string, Colleague) 22 | } 23 | 24 | // Colleague interface 25 | type Colleague interface { 26 | Send(string) 27 | Receive(string) 28 | } 29 | 30 | // ConcreteMediator 31 | type ChatRoom struct { 32 | users []Colleague 33 | } 34 | 35 | func (c *ChatRoom) Register(user Colleague) { 36 | c.users = append(c.users, user) 37 | } 38 | 39 | func (c *ChatRoom) SendMessage(message string, sender Colleague) { 40 | for _, user := range c.users { 41 | if user != sender { 42 | user.Receive(message) 43 | } 44 | } 45 | } 46 | 47 | // ConcreteColleague 48 | type User struct { 49 | name string 50 | chatMed Mediator 51 | } 52 | 53 | func NewUser(name string, chatMed Mediator) *User { 54 | return &User{name: name, chatMed: chatMed} 55 | } 56 | 57 | func (u *User) Send(message string) { 58 | fmt.Printf("%s sends message: %s\n", u.name, message) 59 | u.chatMed.SendMessage(message, u) 60 | } 61 | 62 | func (u *User) Receive(message string) { 63 | fmt.Printf("%s received message: %s\n", u.name, message) 64 | } 65 | ``` 66 | 67 | In this example: 68 | 69 | - `Mediator` is represented by the `Mediator` interface, and `ChatRoom` is the `ConcreteMediator`. 70 | - `Colleague` is represented by the `Colleague` interface, and `User` is the `ConcreteColleague`. 71 | 72 | The `ChatRoom` keeps track of all `User` objects and handles the forwarding of messages between them. Each `User` communicates only with the `ChatRoom`, reducing the coupling between `User` objects. 73 | -------------------------------------------------------------------------------- /behavioral/mediator/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | // Mediator interface 6 | type Mediator interface { 7 | SendMessage(string, Colleague) 8 | } 9 | 10 | // Colleague interface 11 | type Colleague interface { 12 | Send(string) 13 | Receive(string) 14 | } 15 | 16 | // ConcreteMediator 17 | type ChatRoom struct { 18 | users []Colleague 19 | } 20 | 21 | func (c *ChatRoom) Register(user Colleague) { 22 | c.users = append(c.users, user) 23 | } 24 | 25 | func (c *ChatRoom) SendMessage(message string, sender Colleague) { 26 | for _, user := range c.users { 27 | if user != sender { 28 | user.Receive(message) 29 | } 30 | } 31 | } 32 | 33 | // ConcreteColleague 34 | type User struct { 35 | name string 36 | chatMed Mediator 37 | } 38 | 39 | func NewUser(name string, chatMed Mediator) *User { 40 | return &User{name: name, chatMed: chatMed} 41 | } 42 | 43 | func (u *User) Send(message string) { 44 | fmt.Printf("%s sends message: %s\n", u.name, message) 45 | u.chatMed.SendMessage(message, u) 46 | } 47 | 48 | func (u *User) Receive(message string) { 49 | fmt.Printf("%s received message: %s\n", u.name, message) 50 | } 51 | 52 | func main() { 53 | chatroom := &ChatRoom{} 54 | 55 | alice := NewUser("Alice", chatroom) 56 | bob := NewUser("Bob", chatroom) 57 | charlie := NewUser("Charlie", chatroom) 58 | 59 | chatroom.Register(alice) 60 | chatroom.Register(bob) 61 | chatroom.Register(charlie) 62 | 63 | alice.Send("Hi, everyone!") 64 | bob.Send("Hello, Alice!") 65 | charlie.Send("Hey, how are you?") 66 | } 67 | -------------------------------------------------------------------------------- /behavioral/memento/README.md: -------------------------------------------------------------------------------- 1 | # Memento 2 | 3 | The Memento design pattern is a behavioral design pattern that provides the capability to restore an object to its previous state. This pattern is particularly useful when you need to implement features like undo or save functionality. The pattern involves three types of participant classes: 4 | 5 | - **Originator**: The class that has an internal state we wish to save and restore later. 6 | - **Memento**: The class that stores the internal state of the Originator. The state could be saved outside the Originator but without exposing the details. 7 | - **Caretaker**: The class that keeps track of various states of the Originator. It keeps a list of Memento objects to achieve this. 8 | 9 | ## Example 10 | 11 | Let's implement the Memento pattern to maintain the history of a simple text editor, allowing us to undo changes. 12 | 13 | Here is the code in Go: 14 | 15 | ```go 16 | // Originator 17 | type Editor struct { 18 | text string 19 | } 20 | 21 | func (e *Editor) SetText(text string) { 22 | e.text = text 23 | } 24 | 25 | func (e *Editor) CreateSnapshot() *Snapshot { 26 | return &Snapshot{e.text} 27 | } 28 | 29 | func (e *Editor) RestoreSnapshot(s *Snapshot) { 30 | e.text = s.GetText() 31 | } 32 | 33 | // Memento 34 | type Snapshot struct { 35 | text string 36 | } 37 | 38 | func (s *Snapshot) GetText() string { 39 | return s.text 40 | } 41 | 42 | // Caretaker 43 | type History struct { 44 | snapshots []*Snapshot 45 | } 46 | 47 | func (h *History) AddSnapshot(s *Snapshot) { 48 | h.snapshots = append(h.snapshots, s) 49 | } 50 | 51 | func (h *History) Undo() *Snapshot { 52 | length := len(h.snapshots) 53 | 54 | if length < 2 { 55 | return nil // Cannot undo; not enough snapshots 56 | } 57 | 58 | lastSnapshot := h.snapshots[length-2] // Get the second last snapshot 59 | h.snapshots = h.snapshots[:length-1] // Remove the last snapshot 60 | 61 | return lastSnapshot // Return the second last snapshot 62 | } 63 | ``` 64 | 65 | In this example: 66 | 67 | - `Editor` represents the `Originator`. It maintains some text and can produce snapshots (`Memento`) of its current state. 68 | - `Snapshot` represents the `Memento`. It stores a snapshot of the `Editor`'s state. 69 | - `History` is the `Caretaker`. It maintains a history of states that can be used to restore the `Editor` to previous states. 70 | -------------------------------------------------------------------------------- /behavioral/memento/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | // Originator 6 | type Editor struct { 7 | text string 8 | } 9 | 10 | func (e *Editor) SetText(text string) { 11 | e.text = text 12 | } 13 | 14 | func (e *Editor) CreateSnapshot() *Snapshot { 15 | return &Snapshot{e.text} 16 | } 17 | 18 | func (e *Editor) RestoreSnapshot(s *Snapshot) { 19 | e.text = s.GetText() 20 | } 21 | 22 | // Memento 23 | type Snapshot struct { 24 | text string 25 | } 26 | 27 | func (s *Snapshot) GetText() string { 28 | return s.text 29 | } 30 | 31 | // Caretaker 32 | type History struct { 33 | snapshots []*Snapshot 34 | } 35 | 36 | func (h *History) AddSnapshot(s *Snapshot) { 37 | h.snapshots = append(h.snapshots, s) 38 | } 39 | 40 | func (h *History) Undo() *Snapshot { 41 | length := len(h.snapshots) 42 | 43 | if length < 2 { 44 | return nil // Cannot undo; not enough snapshots 45 | } 46 | 47 | lastSnapshot := h.snapshots[length-2] // Get the second last snapshot 48 | h.snapshots = h.snapshots[:length-1] // Remove the last snapshot 49 | 50 | return lastSnapshot // Return the second last snapshot 51 | } 52 | 53 | func main() { 54 | editor := &Editor{} 55 | history := &History{} 56 | 57 | editor.SetText("First line.") 58 | history.AddSnapshot(editor.CreateSnapshot()) 59 | 60 | editor.SetText("Second line.") 61 | history.AddSnapshot(editor.CreateSnapshot()) 62 | 63 | editor.SetText("Third line.") 64 | history.AddSnapshot(editor.CreateSnapshot()) 65 | 66 | fmt.Println("Current Text:", editor.text) 67 | 68 | // Undo to previous state 69 | editor.RestoreSnapshot(history.Undo()) 70 | fmt.Println("Undo 1: ", editor.text) 71 | 72 | // Undo to previous state 73 | editor.RestoreSnapshot(history.Undo()) 74 | fmt.Println("Undo 2: ", editor.text) 75 | 76 | // Undo to previous state; As this is the last state, it should remain the same. 77 | snapshot := history.Undo() 78 | if snapshot != nil { 79 | editor.RestoreSnapshot(snapshot) 80 | } 81 | fmt.Println("Undo 3: ", editor.text) 82 | } 83 | -------------------------------------------------------------------------------- /behavioral/observer/README.md: -------------------------------------------------------------------------------- 1 | # Observer 2 | 3 | The Observer Design Pattern is a behavioral design pattern that allows objects to notify other objects about changes in their state. It establishes a one-to-many dependency between a subject object that holds state, and any number of observer objects that are interested in changes to the subject's state. 4 | 5 | Here's a simple analogy: think of a news publisher and its subscribers. When the publisher releases a new article, it notifies all its subscribers. In this scenario, the publisher is the "subject" and the subscribers are the "observers". This concept of automatically notifying interested parties is the core idea behind the Observer pattern. 6 | 7 | In software, the Observer pattern is commonly used in event-driven systems. You would use the Observer pattern when changes to the state of one object may require changes in other objects, and the actual number of objects is unknown or dynamic. 8 | 9 | Here's a high-level description of the Observer pattern's participants: 10 | 11 | - Subject: This is the object that holds the state. It allows observers to register and unregister their interest. 12 | 13 | - Observer: These are the objects that want to know about changes. They register their interest with the Subject and also define a method for receiving notifications. 14 | 15 | - ConcreteSubject: A concrete subject stores the state of interest to ConcreteObserver objects. When a change occurs in the subject's state, it sends a notification to all registered Observers. 16 | 17 | - ConcreteObserver: A ConcreteObserver maintains a reference to a ConcreteSubject object, stores state that should stay consistent with the subject's, and implements the Observer updating interface to keep its state consistent with the subject's. 18 | 19 | In Go, this pattern could be implemented using interfaces to define the `Subject` and `Observer`, and individual types that implement these interfaces. The Observer's update method would be called when the `Subject` changes. 20 | 21 | ## Example 22 | 23 | Let's consider a scenario where we have a Job Posting site and users can subscribe to be notified when a new job is posted. This is a good example for the Observer pattern as it involves a subject (Job Postings) and observers (Subscribed Users) where observers need to be notified when there's a change in the subject. 24 | 25 | ```go 26 | // JobPost is a struct that represents a job posting 27 | type JobPost struct { 28 | title string 29 | } 30 | 31 | // Observer interface 32 | type Observer interface { 33 | Notify(jobPost JobPost) 34 | } 35 | 36 | // JobSeeker implements Observer 37 | type JobSeeker struct { 38 | name string 39 | } 40 | 41 | func (js *JobSeeker) Notify(jobPost JobPost) { 42 | fmt.Printf("Hi %s! New job posted: %s\n", js.name, jobPost.title) 43 | } 44 | 45 | // JobBoard is our subject struct 46 | type JobBoard struct { 47 | subscribers []Observer 48 | } 49 | 50 | func (jb *JobBoard) Subscribe(observer Observer) { 51 | jb.subscribers = append(jb.subscribers, observer) 52 | } 53 | 54 | func (jb *JobBoard) AddJob(jobPost JobPost) { 55 | for _, subscriber := range jb.subscribers { 56 | subscriber.Notify(jobPost) 57 | } 58 | } 59 | ``` 60 | 61 | When a new job is posted (i.e., the JobBoard's state changes), all the subscribed job seekers are notified. This is the Observer pattern in action. 62 | -------------------------------------------------------------------------------- /behavioral/observer/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | // JobPost is a struct that represents a job posting 6 | type JobPost struct { 7 | title string 8 | } 9 | 10 | // Observer interface 11 | type Observer interface { 12 | Notify(jobPost JobPost) 13 | } 14 | 15 | // JobSeeker implements Observer 16 | type JobSeeker struct { 17 | name string 18 | } 19 | 20 | func (js *JobSeeker) Notify(jobPost JobPost) { 21 | fmt.Printf("Hi %s! New job posted: %s\n", js.name, jobPost.title) 22 | } 23 | 24 | // JobBoard is our subject struct 25 | type JobBoard struct { 26 | subscribers []Observer 27 | } 28 | 29 | func (jb *JobBoard) Subscribe(observer Observer) { 30 | jb.subscribers = append(jb.subscribers, observer) 31 | } 32 | 33 | func (jb *JobBoard) AddJob(jobPost JobPost) { 34 | for _, subscriber := range jb.subscribers { 35 | subscriber.Notify(jobPost) 36 | } 37 | } 38 | 39 | func main() { 40 | // Create subscribers 41 | jobSeeker1 := &JobSeeker{name: "John Doe"} 42 | jobSeeker2 := &JobSeeker{name: "Jane Doe"} 43 | 44 | // Create publisher and add subscribers 45 | jobBoard := &JobBoard{} 46 | jobBoard.Subscribe(jobSeeker1) 47 | jobBoard.Subscribe(jobSeeker2) 48 | 49 | // Add a new job and see if subscribers get notified 50 | jobBoard.AddJob(JobPost{"Software Engineer"}) 51 | } 52 | -------------------------------------------------------------------------------- /behavioral/state/README.md: -------------------------------------------------------------------------------- 1 | # State 2 | 3 | The "state" design pattern allows an object to change its behavior when its internal state changes. In essence, it appears as if the object changed its class. Instead of having a monolithic object that tries to manage every possible state through conditionals or switch statements, the state pattern promotes the idea of encapsulating state-specific behavior into separate state classes. 4 | 5 | Let's look at a basic breakdown: 6 | 7 | - State Interface: Defines an interface to encapsulate the associated behaviors with a particular state of the Context. 8 | - Concrete States: Classes that implement the State interface and provide the behavior specific to a state. 9 | - Context: The main object whose behavior changes based on its current state. 10 | 11 | ## Example 12 | 13 | Let's consider the scenario of an online order system where an order can be in various states, like New, Shipped, Delivered, or Canceled. Depending on the current state of an order, the operations you can perform on it and the transitions to other states might differ. 14 | 15 | ```go 16 | // State interface 17 | type OrderState interface { 18 | ShipOrder() 19 | DeliverOrder() 20 | CancelOrder() 21 | } 22 | 23 | // Concrete States 24 | type NewOrderState struct{} 25 | 26 | func (n *NewOrderState) ShipOrder() { 27 | fmt.Println("Shipping Order.") 28 | } 29 | 30 | func (n *NewOrderState) DeliverOrder() { 31 | fmt.Println("Can't deliver an order which hasn't been shipped!") 32 | } 33 | 34 | func (n *NewOrderState) CancelOrder() { 35 | fmt.Println("Canceling Order.") 36 | } 37 | 38 | type ShippedOrderState struct{} 39 | 40 | func (s *ShippedOrderState) ShipOrder() { 41 | fmt.Println("Can't ship an order again.") 42 | } 43 | 44 | func (s *ShippedOrderState) DeliverOrder() { 45 | fmt.Println("Delivering Order.") 46 | } 47 | 48 | func (s *ShippedOrderState) CancelOrder() { 49 | fmt.Println("Can't cancel a shipped order!") 50 | } 51 | 52 | type DeliveredOrderState struct{} 53 | 54 | func (d *DeliveredOrderState) ShipOrder() { 55 | fmt.Println("Order already delivered.") 56 | } 57 | 58 | func (d *DeliveredOrderState) DeliverOrder() { 59 | fmt.Println("Order already delivered.") 60 | } 61 | 62 | func (d *DeliveredOrderState) CancelOrder() { 63 | fmt.Println("Can't cancel a delivered order!") 64 | } 65 | 66 | // Context 67 | type Order struct { 68 | state OrderState 69 | } 70 | 71 | func (o *Order) ShipOrder() { 72 | o.state.ShipOrder() 73 | } 74 | 75 | func (o *Order) DeliverOrder() { 76 | o.state.DeliverOrder() 77 | } 78 | 79 | func (o *Order) CancelOrder() { 80 | o.state.CancelOrder() 81 | } 82 | 83 | func NewOrder() *Order { 84 | return &Order{state: &NewOrderState{}} 85 | } 86 | ``` 87 | 88 | In this example, the `Order` context delegates all its actions to the current state. Each state class handles its respective logic. If a new state or behavior is introduced, we only need to add or modify the corresponding state class, keeping the `Order` context and other states untouched. This makes the system more maintainable and less error-prone. 89 | -------------------------------------------------------------------------------- /behavioral/state/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | // State interface 6 | type OrderState interface { 7 | ShipOrder() 8 | DeliverOrder() 9 | CancelOrder() 10 | } 11 | 12 | // Concrete States 13 | type NewOrderState struct{} 14 | 15 | func (n *NewOrderState) ShipOrder() { 16 | fmt.Println("Shipping Order.") 17 | } 18 | 19 | func (n *NewOrderState) DeliverOrder() { 20 | fmt.Println("Can't deliver an order which hasn't been shipped!") 21 | } 22 | 23 | func (n *NewOrderState) CancelOrder() { 24 | fmt.Println("Canceling Order.") 25 | } 26 | 27 | type ShippedOrderState struct{} 28 | 29 | func (s *ShippedOrderState) ShipOrder() { 30 | fmt.Println("Can't ship an order again.") 31 | } 32 | 33 | func (s *ShippedOrderState) DeliverOrder() { 34 | fmt.Println("Delivering Order.") 35 | } 36 | 37 | func (s *ShippedOrderState) CancelOrder() { 38 | fmt.Println("Can't cancel a shipped order!") 39 | } 40 | 41 | type DeliveredOrderState struct{} 42 | 43 | func (d *DeliveredOrderState) ShipOrder() { 44 | fmt.Println("Order already delivered.") 45 | } 46 | 47 | func (d *DeliveredOrderState) DeliverOrder() { 48 | fmt.Println("Order already delivered.") 49 | } 50 | 51 | func (d *DeliveredOrderState) CancelOrder() { 52 | fmt.Println("Can't cancel a delivered order!") 53 | } 54 | 55 | // Context 56 | type Order struct { 57 | state OrderState 58 | } 59 | 60 | func (o *Order) ShipOrder() { 61 | o.state.ShipOrder() 62 | } 63 | 64 | func (o *Order) DeliverOrder() { 65 | o.state.DeliverOrder() 66 | } 67 | 68 | func (o *Order) CancelOrder() { 69 | o.state.CancelOrder() 70 | } 71 | 72 | func NewOrder() *Order { 73 | return &Order{state: &NewOrderState{}} 74 | } 75 | 76 | func main() { 77 | order := NewOrder() 78 | order.ShipOrder() 79 | order.DeliverOrder() 80 | 81 | // Setting a new state manually just for demonstration. 82 | order.state = &ShippedOrderState{} 83 | order.CancelOrder() 84 | } 85 | -------------------------------------------------------------------------------- /behavioral/strategy/README.md: -------------------------------------------------------------------------------- 1 | # Strategy 2 | 3 | The Strategy design pattern is a behavioral design pattern that lets the algorithm vary independently from the clients that use it. It defines a family of algorithms, encapsulates each one, and makes them interchangeable. 4 | 5 | The strategy pattern involves using an interface to abstractly define an operation that needs to be carried out. Concrete implementations of the interface will encapsulate different strategies or ways to carry out the operation. 6 | 7 | The object that uses the strategy pattern will maintain a reference to a Strategy object and will communicate with this object only through the strategy interface. 8 | 9 | The advantage of the strategy pattern is that it promotes algorithmic independence. It decouples the behavior of an object from the object itself. 10 | 11 | Here's the general structure of Strategy design pattern: 12 | 13 | - Strategy (interface): This is an interface used to abstractly define the operation(s) that we're planning to implement with different strategies. 14 | 15 | - ConcreteStrategy (class): This is a class that implements the Strategy interface, providing its own version of the interface method(s). 16 | 17 | - Context (class): This is a class that uses a strategy to do something. It interacts with a strategy through the Strategy interface only, meaning it's decoupled from the ConcreteStrategy. 18 | 19 | This pattern can be beneficial when we need to select an algorithm at runtime. It's also helpful when we have a lot of similar classes that only differ in their behaviors. Instead of implementing many versions of your class with different behaviors, you can separate the behaviors as strategies and use the same context class in all versions. 20 | 21 | ## Example 22 | 23 | Let's use the Strategy pattern to select between a Bubble sort and a Quick sort strategy at runtime: 24 | 25 | ```go 26 | // SortStrategy defines the method for sorting 27 | type SortStrategy interface { 28 | Sort([]int) []int 29 | } 30 | 31 | // BubbleSortStrategy uses bubble sort algorithm for sorting 32 | type BubbleSortStrategy struct{} 33 | 34 | func (b *BubbleSortStrategy) Sort(input []int) []int { 35 | n := len(input) 36 | sorted := make([]int, n) 37 | copy(sorted, input) 38 | 39 | for i := 0; i < n; i++ { 40 | for j := 0; j < n-i-1; j++ { 41 | if sorted[j] > sorted[j+1] { 42 | sorted[j], sorted[j+1] = sorted[j+1], sorted[j] 43 | } 44 | } 45 | } 46 | 47 | return sorted 48 | } 49 | 50 | // QuickSortStrategy uses quick sort algorithm for sorting 51 | type QuickSortStrategy struct{} 52 | 53 | func (q *QuickSortStrategy) Sort(input []int) []int { 54 | sorted := make([]int, len(input)) 55 | copy(sorted, input) 56 | sort.Ints(sorted) 57 | return sorted 58 | } 59 | 60 | // SortingContext is the context that uses the strategy 61 | type SortingContext struct { 62 | strategy SortStrategy 63 | } 64 | 65 | func (s *SortingContext) SetStrategy(strategy SortStrategy) { 66 | s.strategy = strategy 67 | } 68 | 69 | func (s *SortingContext) ExecuteStrategy(input []int) []int { 70 | return s.strategy.Sort(input) 71 | } 72 | ``` 73 | 74 | In the example above, `SortStrategy` is the strategy interface, `BubbleSortStrategy` and `QuickSortStrategy` are concrete strategies, and `SortingContext` is the context. Depending on what we set as the `SortStrategy`, the appropriate sorting algorithm will be applied. 75 | -------------------------------------------------------------------------------- /behavioral/strategy/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | "sort" 6 | ) 7 | 8 | // SortStrategy defines the method for sorting 9 | type SortStrategy interface { 10 | Sort([]int) []int 11 | } 12 | 13 | // BubbleSortStrategy uses bubble sort algorithm for sorting 14 | type BubbleSortStrategy struct{} 15 | 16 | func (b *BubbleSortStrategy) Sort(input []int) []int { 17 | n := len(input) 18 | sorted := make([]int, n) 19 | copy(sorted, input) 20 | 21 | for i := 0; i < n; i++ { 22 | for j := 0; j < n-i-1; j++ { 23 | if sorted[j] > sorted[j+1] { 24 | sorted[j], sorted[j+1] = sorted[j+1], sorted[j] 25 | } 26 | } 27 | } 28 | 29 | return sorted 30 | } 31 | 32 | // QuickSortStrategy uses quick sort algorithm for sorting 33 | type QuickSortStrategy struct{} 34 | 35 | func (q *QuickSortStrategy) Sort(input []int) []int { 36 | sorted := make([]int, len(input)) 37 | copy(sorted, input) 38 | sort.Ints(sorted) 39 | return sorted 40 | } 41 | 42 | // SortingContext is the context that uses the strategy 43 | type SortingContext struct { 44 | strategy SortStrategy 45 | } 46 | 47 | func (s *SortingContext) SetStrategy(strategy SortStrategy) { 48 | s.strategy = strategy 49 | } 50 | 51 | func (s *SortingContext) ExecuteStrategy(input []int) []int { 52 | return s.strategy.Sort(input) 53 | } 54 | 55 | func main() { 56 | data := []int{64, 34, 25, 12, 22, 11, 90} 57 | context := &SortingContext{} 58 | 59 | context.SetStrategy(&BubbleSortStrategy{}) 60 | sortedData := context.ExecuteStrategy(data) 61 | fmt.Println("Bubble Sorted Data: ", sortedData) 62 | 63 | context.SetStrategy(&QuickSortStrategy{}) 64 | sortedData = context.ExecuteStrategy(data) 65 | fmt.Println("Quick Sorted Data: ", sortedData) 66 | } 67 | -------------------------------------------------------------------------------- /behavioral/template/README.md: -------------------------------------------------------------------------------- 1 | # Template 2 | 3 | The "Template" design pattern defines the program skeleton of an algorithm in an algorithm class but delays some steps to subclasses. It lets one redefine certain steps of an algorithm without changing the algorithm's structure. 4 | 5 | Basically, the pattern involves two main components: 6 | 7 | - Abstract Class: Defines abstract placeholder operations (primitive operations), concrete operations, and a template method. 8 | - Concrete Class: Implements the placeholder operations. 9 | 10 | The template method in the abstract class defines the structure of an algorithm and calls placeholder operations as well as concrete operations. 11 | 12 | ## Example 13 | 14 | The Template pattern is especially useful in software development scenarios where there's a clear sequence of steps to be performed, but the specifics of each step might vary. 15 | 16 | Consider the example of a build tool for various project types. Suppose there's a general sequence of steps for building a software project: 17 | 18 | - Load configuration. 19 | - Fetch dependencies. 20 | - Compile source code. 21 | - Run tests. 22 | - Package for deployment. 23 | - While the sequence remains consistent, the specifics of each step can vary depending on the project type (e.g., a Java project vs. a Go project). 24 | 25 | Let's demonstrate this with the Template pattern in Go: 26 | 27 | ```go 28 | // BuildProcess defines the steps of building a software project 29 | type BuildProcess interface { 30 | LoadConfiguration() 31 | FetchDependencies() 32 | Compile() 33 | RunTests() 34 | Package() 35 | } 36 | 37 | // The template method 38 | func Build(p BuildProcess) { 39 | p.LoadConfiguration() 40 | p.FetchDependencies() 41 | p.Compile() 42 | p.RunTests() 43 | p.Package() 44 | } 45 | 46 | type JavaProject struct{} 47 | 48 | func (j *JavaProject) LoadConfiguration() { 49 | fmt.Println("Loading Maven configuration...") 50 | } 51 | 52 | func (j *JavaProject) FetchDependencies() { 53 | fmt.Println("Fetching Maven dependencies...") 54 | } 55 | 56 | func (j *JavaProject) Compile() { 57 | fmt.Println("Compiling Java source files...") 58 | } 59 | 60 | func (j *JavaProject) RunTests() { 61 | fmt.Println("Running JUnit tests...") 62 | } 63 | 64 | func (j *JavaProject) Package() { 65 | fmt.Println("Packaging into a JAR file...") 66 | } 67 | 68 | type GoProject struct{} 69 | 70 | func (g *GoProject) LoadConfiguration() { 71 | fmt.Println("Loading Go modules configuration...") 72 | } 73 | 74 | func (g *GoProject) FetchDependencies() { 75 | fmt.Println("Fetching Go dependencies...") 76 | } 77 | 78 | func (g *GoProject) Compile() { 79 | fmt.Println("Building Go binary...") 80 | } 81 | 82 | func (g *GoProject) RunTests() { 83 | fmt.Println("Running Go tests...") 84 | } 85 | 86 | func (g *GoProject) Package() { 87 | fmt.Println("Packaging Go binary for deployment...") 88 | } 89 | ``` 90 | 91 | In this example: 92 | 93 | - BuildProcess serves as our "abstract class", defining the sequence for building software projects. 94 | - Build is our template method, defining the standard order in which these methods should be called. 95 | - JavaProject and GoProject are our concrete classes, implementing the steps of the build process for Java and Go projects, respectively. 96 | 97 | This design makes it easy to introduce a build process for a new language or framework. Just implement the BuildProcess interface for the new project type and let the Build function handle the sequence. 98 | -------------------------------------------------------------------------------- /behavioral/template/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | // BuildProcess defines the steps of building a software project 6 | type BuildProcess interface { 7 | LoadConfiguration() 8 | FetchDependencies() 9 | Compile() 10 | RunTests() 11 | Package() 12 | } 13 | 14 | // The template method 15 | func Build(p BuildProcess) { 16 | p.LoadConfiguration() 17 | p.FetchDependencies() 18 | p.Compile() 19 | p.RunTests() 20 | p.Package() 21 | } 22 | 23 | type JavaProject struct{} 24 | 25 | func (j *JavaProject) LoadConfiguration() { 26 | fmt.Println("Loading Maven configuration...") 27 | } 28 | 29 | func (j *JavaProject) FetchDependencies() { 30 | fmt.Println("Fetching Maven dependencies...") 31 | } 32 | 33 | func (j *JavaProject) Compile() { 34 | fmt.Println("Compiling Java source files...") 35 | } 36 | 37 | func (j *JavaProject) RunTests() { 38 | fmt.Println("Running JUnit tests...") 39 | } 40 | 41 | func (j *JavaProject) Package() { 42 | fmt.Println("Packaging into a JAR file...") 43 | } 44 | 45 | type GoProject struct{} 46 | 47 | func (g *GoProject) LoadConfiguration() { 48 | fmt.Println("Loading Go modules configuration...") 49 | } 50 | 51 | func (g *GoProject) FetchDependencies() { 52 | fmt.Println("Fetching Go dependencies...") 53 | } 54 | 55 | func (g *GoProject) Compile() { 56 | fmt.Println("Building Go binary...") 57 | } 58 | 59 | func (g *GoProject) RunTests() { 60 | fmt.Println("Running Go tests...") 61 | } 62 | 63 | func (g *GoProject) Package() { 64 | fmt.Println("Packaging Go binary for deployment...") 65 | } 66 | 67 | func main() { 68 | java := &JavaProject{} 69 | Build(java) 70 | 71 | fmt.Println("---") 72 | 73 | golang := &GoProject{} 74 | Build(golang) 75 | } 76 | -------------------------------------------------------------------------------- /behavioral/visitor/README.md: -------------------------------------------------------------------------------- 1 | # Visitor 2 | 3 | The Visitor design pattern is a behavioral design pattern that allows you to add further operations to objects without modifying the classes of the objects you're working with. It allows you to define a new operation without altering the classes of the elements on which it operates. This pattern can be particularly useful when dealing with a structure composed of a mixture of different types of objects and you want to perform operations that depend on the concrete classes of these objects. 4 | 5 | ### Participants 6 | 7 | - **Visitor**: This is an interface that declares a visit operation for each type of concrete element in the object structure. 8 | - **ConcreteVisitor**: This class implements the Visitor interface and defines the operations to be performed on each type of element. 9 | - **Element**: This is an interface that declares an `Accept` method that accepts a visitor. 10 | - **ConcreteElement**: This class implements the Element interface and allows the visitor to visit it. 11 | 12 | ## Example 13 | 14 | The Visitor pattern is often used in cases where you have a complex data structure, like an Abstract Syntax Tree (AST) in a compiler, or a Document Object Model (DOM) in a web browser. The Visitor pattern allows you to extend functionalities without modifying these structures. 15 | 16 | An Abstract Syntax Tree (AST) is a tree representation of the syntactic structure of source code written in a programming language. Each node in the tree denotes a construct in the language. It's "abstract" in the sense that it omits certain syntax rules that aren't necessary for understanding the program's structure. For example, grouping parentheses might be omitted because the structure of the tree makes the execution order of operations clear. 17 | 18 | ### Components 19 | 20 | - **Node**: Each node represents a language construct. For example, a node could represent an arithmetic operation like addition, a control flow construct like a `for` loop, or a data construct like an array. 21 | 22 | - **Edge**: Edges in an AST represent the relationship between the nodes. For example, an edge from an "If statement" node to a "Boolean expression" node signifies that the Boolean expression is a condition for the If statement. 23 | 24 | - **Root**: The root of the tree represents the entire program or the start symbol in the grammar of the programming language. 25 | 26 | ### Use Cases 27 | 28 | 1. **Compilers**: The front end of a compiler usually transforms source code into an AST as an intermediate step in translating code into machine language or bytecode. 29 | 30 | 2. **Code Analysis**: Tools that perform static code analysis often use ASTs to understand the structure of the code. 31 | 32 | 3. **Refactoring**: Code refactoring tools use ASTs to accurately transform the structure of the code. 33 | 34 | 4. **Syntax Highlighting**: Some advanced text editors use ASTs for better syntax highlighting. 35 | 36 | 37 | Consider a simple arithmetic expression `1 + 2 * 3`. An AST representing this expression might look like this: 38 | 39 | ``` 40 | [+] 41 | / \ 42 | [1] [*] 43 | / \ 44 | [2] [3] 45 | ``` 46 | 47 | Here, the root node represents the `+` operation. The left child is `1` and the right child is another operation `*`. This tree structure makes it clear that `2 * 3` should be evaluated first, and then added to `1`, adhering to the rules of arithmetic. 48 | 49 | Let's consider a simplified version of an AST. Assume that we have two types of expressions: `Literal` expressions (just numbers) and `Addition` expressions (which add two other expressions together). Now, imagine we want to perform multiple operations on these expressions: evaluate them to get a result and convert them to a string in infix notation. 50 | 51 | Here's how you could use the Visitor pattern to implement this in Go: 52 | 53 | ```go 54 | // Expression is the 'Element' interface 55 | type Expression interface { 56 | Accept(Visitor) string 57 | } 58 | 59 | // Visitor interface 60 | type Visitor interface { 61 | VisitLiteral(*Literal) string 62 | VisitAddition(*Addition) string 63 | } 64 | 65 | // Literal is a 'ConcreteElement' 66 | type Literal struct { 67 | value int 68 | } 69 | 70 | func (l *Literal) Accept(visitor Visitor) string { 71 | return visitor.VisitLiteral(l) 72 | } 73 | 74 | // Addition is another 'ConcreteElement' 75 | type Addition struct { 76 | left, right Expression 77 | } 78 | 79 | func (a *Addition) Accept(visitor Visitor) string { 80 | return visitor.VisitAddition(a) 81 | } 82 | 83 | // Evaluator is a 'ConcreteVisitor' that evaluates expressions 84 | type Evaluator struct{} 85 | 86 | func (e *Evaluator) VisitLiteral(l *Literal) string { 87 | return strconv.Itoa(l.value) 88 | } 89 | 90 | func (e *Evaluator) VisitAddition(a *Addition) string { 91 | left := a.left.Accept(e) 92 | right := a.right.Accept(e) 93 | return fmt.Sprintf("(%s + %s)", left, right) 94 | } 95 | 96 | // Renderer is another 'ConcreteVisitor' that converts expressions to strings 97 | type Renderer struct{} 98 | 99 | func (r *Renderer) VisitLiteral(l *Literal) string { 100 | return strconv.Itoa(l.value) 101 | } 102 | 103 | func (r *Renderer) VisitAddition(a *Addition) string { 104 | left := a.left.Accept(r) 105 | right := a.right.Accept(r) 106 | return fmt.Sprintf("(%s + %s)", left, right) 107 | } 108 | ``` 109 | 110 | In this example: 111 | 112 | - `Expression` is the Element interface that declares an `Accept` method to accept a visitor. 113 | - `Literal` and `Addition` are Concrete Elements that represent literal numbers and addition operations, respectively. 114 | - `Visitor` is the Visitor interface that declares `VisitLiteral` and `VisitAddition` methods. 115 | - `Evaluator` and `Renderer` are Concrete Visitors. `Evaluator` evaluates expressions, and `Renderer` converts them to strings. 116 | 117 | This example is a simplified AST, but the Visitor pattern makes it easy to add new operations (like optimization, code generation, etc.) without changing the `Expression`, `Literal`, or `Addition` classes. It's particularly useful in software engineering scenarios like compilers and data transformation pipelines. 118 | -------------------------------------------------------------------------------- /behavioral/visitor/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | "strconv" 6 | ) 7 | 8 | // Expression is the 'Element' interface 9 | type Expression interface { 10 | Accept(Visitor) string 11 | } 12 | 13 | // Visitor interface 14 | type Visitor interface { 15 | VisitLiteral(*Literal) string 16 | VisitAddition(*Addition) string 17 | } 18 | 19 | // Literal is a 'ConcreteElement' 20 | type Literal struct { 21 | value int 22 | } 23 | 24 | func (l *Literal) Accept(visitor Visitor) string { 25 | return visitor.VisitLiteral(l) 26 | } 27 | 28 | // Addition is another 'ConcreteElement' 29 | type Addition struct { 30 | left, right Expression 31 | } 32 | 33 | func (a *Addition) Accept(visitor Visitor) string { 34 | return visitor.VisitAddition(a) 35 | } 36 | 37 | // Evaluator is a 'ConcreteVisitor' that evaluates expressions 38 | type Evaluator struct{} 39 | 40 | func (e *Evaluator) VisitLiteral(l *Literal) string { 41 | return strconv.Itoa(l.value) 42 | } 43 | 44 | func (e *Evaluator) VisitAddition(a *Addition) string { 45 | left := a.left.Accept(e) 46 | right := a.right.Accept(e) 47 | return fmt.Sprintf("(%s + %s)", left, right) 48 | } 49 | 50 | // Renderer is another 'ConcreteVisitor' that converts expressions to strings 51 | type Renderer struct{} 52 | 53 | func (r *Renderer) VisitLiteral(l *Literal) string { 54 | return strconv.Itoa(l.value) 55 | } 56 | 57 | func (r *Renderer) VisitAddition(a *Addition) string { 58 | left := a.left.Accept(r) 59 | right := a.right.Accept(r) 60 | return fmt.Sprintf("(%s + %s)", left, right) 61 | } 62 | 63 | func main() { 64 | // Create an AST for the expression: (1 + (2 + 3)) 65 | expression := &Addition{ 66 | left: &Literal{value: 1}, 67 | right: &Addition{left: &Literal{value: 2}, right: &Literal{value: 3}}, 68 | } 69 | 70 | // Evaluate the expression 71 | evaluator := &Evaluator{} 72 | result := expression.Accept(evaluator) 73 | fmt.Printf("Evaluation: %s\n", result) 74 | 75 | // Render the expression 76 | renderer := &Renderer{} 77 | result = expression.Accept(renderer) 78 | fmt.Printf("Rendering: %s\n", result) 79 | } 80 | -------------------------------------------------------------------------------- /creational/abstract_factory/README.md: -------------------------------------------------------------------------------- 1 | # Abstract factory 2 | 3 | The Abstract Factory Design Pattern is a creational pattern that provides an interface for creating families of related or dependent objects without specifying their concrete classes. 4 | 5 | In other words, an abstract factory is a factory of factories. With this pattern, a high level interface is provided that encapsulates a group of factories which share common themes without specifying concrete classes. These factories produce families of related products. 6 | 7 | This pattern is typically implemented via a master factory (the abstract factory) which is capable of creating other factories, which in turn, produce products within the same family. 8 | 9 | # Example 10 | 11 | Imagine we have a UI library, and we want it to support multiple themes (like Light and Dark). Different themes have different styles for the same type of components (like buttons, menus, etc.). 12 | 13 | ```go 14 | // Abstract product 15 | type Button interface { 16 | Render() string 17 | } 18 | 19 | // Concrete product: LightButton 20 | type LightButton struct{} 21 | 22 | func (b LightButton) Render() string { 23 | return "Rendering light theme button." 24 | } 25 | 26 | // Concrete product: DarkButton 27 | type DarkButton struct{} 28 | 29 | func (b DarkButton) Render() string { 30 | return "Rendering dark theme button." 31 | } 32 | 33 | // Abstract factory 34 | type UIFactory interface { 35 | CreateButton() Button 36 | } 37 | 38 | // Concrete factory: LightThemeFactory 39 | type LightThemeFactory struct{} 40 | 41 | func (f LightThemeFactory) CreateButton() Button { 42 | return LightButton{} 43 | } 44 | 45 | // Concrete factory: DarkThemeFactory 46 | type DarkThemeFactory struct{} 47 | 48 | func (f DarkThemeFactory) CreateButton() Button { 49 | return DarkButton{} 50 | } 51 | ``` 52 | 53 | Here, `UIFactory` is the abstract factory. `LightThemeFactory` and `DarkThemeFactory` are its concrete factories. `Button` is the abstract product. `LightButton` and `DarkButton` are its concrete products. 54 | 55 | We can add more methods to the UIFactory to create other types of UI components (like `CreateMenu`, `CreateToolbar`, etc.), and more themes by adding more concrete factories. 56 | 57 | This pattern is especially useful when a system should be independent of how its products are created, composed, and represented, and when a family of related product objects is designed to be used together. 58 | -------------------------------------------------------------------------------- /creational/abstract_factory/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | ) 6 | 7 | type Button interface { 8 | Render() string 9 | } 10 | 11 | type LightButton struct{} 12 | 13 | func (b LightButton) Render() string { 14 | return "Rendering light theme button." 15 | } 16 | 17 | type DarkButton struct{} 18 | 19 | func (b DarkButton) Render() string { 20 | return "Rendering dark theme button." 21 | } 22 | 23 | type UIFactory interface { 24 | CreateButton() Button 25 | } 26 | 27 | type LightThemeFactory struct{} 28 | 29 | func (f LightThemeFactory) CreateButton() Button { 30 | return LightButton{} 31 | } 32 | 33 | type DarkThemeFactory struct{} 34 | 35 | func (f DarkThemeFactory) CreateButton() Button { 36 | return DarkButton{} 37 | } 38 | 39 | func main() { 40 | var factory UIFactory 41 | var button Button 42 | 43 | // Select the factory based on user preference or config file, for example: 44 | userPrefersDarkMode := true // Imagine this value is from user settings 45 | 46 | if userPrefersDarkMode { 47 | factory = DarkThemeFactory{} 48 | } else { 49 | factory = LightThemeFactory{} 50 | } 51 | 52 | // Create a button using the factory 53 | button = factory.CreateButton() 54 | 55 | // Use the button 56 | fmt.Println(button.Render()) 57 | } 58 | -------------------------------------------------------------------------------- /creational/builder/README.md: -------------------------------------------------------------------------------- 1 | # Builder 2 | 3 | The Builder Design Pattern is a creational pattern that is used to construct a complex object step by step. It separates the construction of an object from its representation so that the same construction process can create different representations. 4 | 5 | When you are building a complex object that has multiple parts or configuration options, creating and configuring the object directly within client code or via a constructor can become unwieldy and hard to read. The Builder pattern addresses this issue by providing a way to build the complex object step by step, with each step clearly encapsulated by a method in the builder. 6 | 7 | ## Example 8 | 9 | The Builder pattern is most useful when dealing with a complex object that requires a significant or complex process to construct. It's often employed in contexts where objects are built from a variety of parts that need to be created and assembled. It's also particularly helpful when you might have multiple representations of an object, or when you want to encapsulate the creation logic separate from the main application. 10 | 11 | In this example, `RequestBuilder` is used to construct a complex `http.Request` object. Each Set method in the builder sets a different attribute of the request and returns the builder itself, allowing the methods to be chained. The `Build` method is finally used to construct the `http.Request` object. This approach can make the creation of complex request objects more manageable and readable. 12 | -------------------------------------------------------------------------------- /creational/builder/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | "net/http" 6 | "strings" 7 | ) 8 | 9 | type RequestBuilder struct { 10 | Method string 11 | URL string 12 | Header http.Header 13 | Body string 14 | } 15 | 16 | func NewRequestBuilder() *RequestBuilder { 17 | return &RequestBuilder{ 18 | Header: make(http.Header), 19 | } 20 | } 21 | 22 | func (b *RequestBuilder) SetMethod(method string) *RequestBuilder { 23 | b.Method = strings.ToUpper(method) 24 | return b 25 | } 26 | 27 | func (b *RequestBuilder) SetURL(url string) *RequestBuilder { 28 | b.URL = url 29 | return b 30 | } 31 | 32 | func (b *RequestBuilder) SetHeader(key, value string) *RequestBuilder { 33 | b.Header.Add(key, value) 34 | return b 35 | } 36 | 37 | func (b *RequestBuilder) SetBody(body string) *RequestBuilder { 38 | b.Body = body 39 | return b 40 | } 41 | 42 | func (b *RequestBuilder) Build() (*http.Request, error) { 43 | req, err := http.NewRequest(b.Method, b.URL, strings.NewReader(b.Body)) 44 | if err != nil { 45 | return nil, err 46 | } 47 | 48 | req.Header = b.Header 49 | 50 | return req, nil 51 | } 52 | 53 | func main() { 54 | builder := NewRequestBuilder(). 55 | SetMethod("POST"). 56 | SetURL("http://example.com"). 57 | SetHeader("Content-Type", "application/json"). 58 | SetBody(`{"key": "value"}`) 59 | 60 | req, err := builder.Build() 61 | if err != nil { 62 | panic(err) 63 | } 64 | 65 | fmt.Printf("%+v\n", req) // This prints the request object 66 | } 67 | -------------------------------------------------------------------------------- /creational/factory/README.md: -------------------------------------------------------------------------------- 1 | # Factory 2 | 3 | The Factory Method Design Pattern is a creational pattern that provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created. This pattern is used when a class cannot anticipate the class of objects it needs to create. 4 | 5 | The Factory pattern is often used in situations where a system should be independent of how its objects are created, composed, and represented. It provides a simple way of decoupling the concrete objects from the parts of the system that use them. 6 | 7 | A factory method in a class is a method that returns objects of a varying prototype or class from some method call, which is assumed to be "new". The factories are a great way to implement the concept of abstraction by encapsulating the responsibilities of creating and initializing complex objects. 8 | 9 | ## Example 10 | 11 | In this example, we have a `Logger` interface that different types of loggers (like `ConsoleLogger` and `FileLogger`) implement. The `LoggerFactory` can create different types of loggers depending on the argument passed to `CreateLogger`. 12 | 13 | ```go 14 | type Logger interface { 15 | Log(message string) 16 | } 17 | 18 | type ConsoleLogger struct{} 19 | 20 | func (cl *ConsoleLogger) Log(message string) { 21 | fmt.Println(message) 22 | } 23 | 24 | type FileLogger struct { 25 | file *os.File 26 | } 27 | 28 | func (fl *FileLogger) Log(message string) { 29 | fmt.Fprintln(fl.file, message) 30 | } 31 | 32 | type LoggerFactory struct{} 33 | 34 | func (lf *LoggerFactory) CreateLogger(loggerType string) (Logger, error) { 35 | switch loggerType { 36 | case "console": 37 | return &ConsoleLogger{}, nil 38 | case "file": 39 | file, err := os.Create("log.txt") 40 | if err != nil { 41 | return nil, err 42 | } 43 | return &FileLogger{file: file}, nil 44 | default: 45 | return nil, fmt.Errorf("unsupported logger type") 46 | } 47 | } 48 | ``` 49 | 50 | This could be part of a larger logging library where you can choose between different types of loggers depending on your requirements. For example, you might use a `ConsoleLogger` in a development environment to print logs for debugging, but in a production environment, you might use a `FileLogger` or maybe a `DatabaseLogger` to store logs more permanently. 51 | -------------------------------------------------------------------------------- /creational/factory/log.txt: -------------------------------------------------------------------------------- 1 | Hello from file logger! 2 | -------------------------------------------------------------------------------- /creational/factory/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | "os" 6 | ) 7 | 8 | type Logger interface { 9 | Log(message string) 10 | } 11 | 12 | type ConsoleLogger struct{} 13 | 14 | func (cl *ConsoleLogger) Log(message string) { 15 | fmt.Println(message) 16 | } 17 | 18 | type FileLogger struct { 19 | file *os.File 20 | } 21 | 22 | func (fl *FileLogger) Log(message string) { 23 | fmt.Fprintln(fl.file, message) 24 | } 25 | 26 | type LoggerFactory struct{} 27 | 28 | func (lf *LoggerFactory) CreateLogger(loggerType string) (Logger, error) { 29 | switch loggerType { 30 | case "console": 31 | return &ConsoleLogger{}, nil 32 | case "file": 33 | file, err := os.Create("log.txt") 34 | if err != nil { 35 | return nil, err 36 | } 37 | return &FileLogger{file: file}, nil 38 | default: 39 | return nil, fmt.Errorf("unsupported logger type") 40 | } 41 | } 42 | 43 | func main() { 44 | loggerFactory := &LoggerFactory{} 45 | 46 | logger, err := loggerFactory.CreateLogger("console") 47 | if err != nil { 48 | panic(err) 49 | } 50 | logger.Log("Hello from console logger!") 51 | 52 | logger, err = loggerFactory.CreateLogger("file") 53 | if err != nil { 54 | panic(err) 55 | } 56 | logger.Log("Hello from file logger!") 57 | } 58 | -------------------------------------------------------------------------------- /creational/prototype/README.md: -------------------------------------------------------------------------------- 1 | # Prototype 2 | 3 | The prototype design pattern involves creating objects based on a template of an existing object through cloning. It is especially useful when the construction of a new object is inefficient or complex. 4 | 5 | In the prototype pattern, an instance of actual object (which is created by expensive database operation) is cloned to create a new object. This pattern provides a mechanism to copy the original object to a new object and then modify it according to our needs. 6 | 7 | This pattern involves implementing a prototype interface which tells to create a clone of the current object. It is used when creation of object directly is costly. So instead of creating a costly object, an existing object is copied. 8 | 9 | In Go, this can be implemented by using the `Clone` method in an interface that all the struct who want to use the Prototype pattern needs to implement. The `Clone` method will return an instance of itself. 10 | 11 | ## Example 12 | 13 | Let's imagine you're developing an application where you're dealing with different types of `Form` objects, each representing a form in a web application with many pre-filled fields. Each Form object is expensive to create (imagine it makes a network request or a database query to populate some of its fields). Therefore, instead of creating a new Form object each time a user visits a form, you might want to clone a pre-populated prototype. 14 | 15 | ```go 16 | // RegistrationForm is a concrete type implementing Form 17 | type RegistrationForm struct { 18 | Name string 19 | Email string 20 | } 21 | 22 | // Clone method for RegistrationForm 23 | func (r *RegistrationForm) Clone() Form { 24 | return &RegistrationForm{ 25 | Name: r.Name, 26 | Email: r.Email, 27 | } 28 | } 29 | ``` 30 | 31 | In this example, when a new `RegistrationForm` is needed, instead of creating a new one from scratch (which may be expensive due to required default data), we clone a pre-populated `RegistrationForm`. The `Clone` function allows each type of form to specify how it should be copied, providing a lot of flexibility. In the real world, the `Clone` method could handle deep copying and other complex copying logic. 32 | 33 | While it might seem unnecessary for a simple example like this, in a larger, more complex system, creating a new instance of an object can sometimes be a relatively expensive operation in terms of resources. 34 | 35 | Consider a case where the constructor of a class makes a call to a database, retrieves a large amount of data, and populates a complex object graph. In this case, creating a new instance is a time and resource-consuming operation. 36 | 37 | Now, suppose we often need to create objects that are identical or slightly different. In this case, it's much more efficient to clone the existing instance and modify it as needed, rather than creating a new one from scratch. 38 | 39 | In the Prototype design pattern, the `Clone` method isn't just copying the fields of an object. It could also be handling some more complex operations that are required to correctly copy an object, such as deep copying and managing references. 40 | 41 | Again, whether or not to use the Prototype pattern or simply clone/copy an object depends on the specific needs and constraints of your project. In many cases, especially for simple objects, a straightforward copy or a new object instantiation is preferable and leads to more readable code. However, in some scenarios where object creation is resource-intensive, the Prototype pattern can be a good approach. 42 | -------------------------------------------------------------------------------- /creational/prototype/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | // Form - our prototype interface 6 | type Form interface { 7 | Clone() Form 8 | } 9 | 10 | // RegistrationForm is a concrete type implementing Form 11 | type RegistrationForm struct { 12 | Name string 13 | Email string 14 | } 15 | 16 | // Clone method for RegistrationForm 17 | func (r *RegistrationForm) Clone() Form { 18 | return &RegistrationForm{ 19 | Name: r.Name, 20 | Email: r.Email, 21 | } 22 | } 23 | 24 | func main() { 25 | // create a prototype of the RegistrationForm 26 | prototype := &RegistrationForm{ 27 | Name: "Default Name", 28 | Email: "default@example.com", 29 | } 30 | 31 | // use the prototype to clone a new form 32 | clonedForm := prototype.Clone() 33 | 34 | // type assertion to RegistrationForm 35 | regForm, ok := clonedForm.(*RegistrationForm) 36 | if !ok { 37 | fmt.Println("Type assertion to RegistrationForm failed") 38 | return 39 | } 40 | 41 | fmt.Printf("Name: %s, Email: %s\n", regForm.Name, regForm.Email) 42 | } 43 | -------------------------------------------------------------------------------- /creational/singleton/README.md: -------------------------------------------------------------------------------- 1 | # Singleton 2 | 3 | The Singleton pattern is a design pattern that restricts the instantiation of a class to a single instance. This is useful when exactly one object is needed to coordinate actions across the system. 4 | 5 | The Singleton pattern is used for logging, driver objects, caching, thread pools, and database connections. It is a relatively simple pattern, but it comes with its own set of complications. The main issue is that it introduces global state into an application. For this reason, it's generally not considered a good practice to use singletons in a system that you want to be easy to test and maintain. However, it can be useful in certain scenarios where you need to coordinate logic in a globally accessible way. 6 | 7 | ## Example 8 | 9 | The singleton `WorkerPool` is the focus of this example. It's a structure containing a pool of workers, a pool of jobs and a `WaitGroup`. 10 | 11 | ```go 12 | type WorkerPool struct { 13 | workers []*Worker 14 | jobQueue chan Job 15 | workerPool chan chan Job 16 | wg sync.WaitGroup 17 | } 18 | ``` 19 | 20 | Each `Worker` has a job channel to receive jobs and a quit channel for termination. When the worker is started, it continually listens on its job channel for incoming jobs and signals the `WaitGroup` when the job is done. When it receives a job, it prints a message. If it receives a signal on the quit channel, it stops. 21 | 22 | ```go 23 | type Worker struct { 24 | ID int 25 | WorkerPool chan chan Job 26 | JobChannel chan Job 27 | quit chan bool 28 | } 29 | 30 | func NewWorker(workerPool chan chan Job, id int) *Worker { 31 | return &Worker{ 32 | ID: id, 33 | WorkerPool: workerPool, 34 | JobChannel: make(chan Job), 35 | quit: make(chan bool), 36 | } 37 | } 38 | 39 | func (w *Worker) Start(wg *sync.WaitGroup) { 40 | go func() { 41 | for { 42 | w.WorkerPool <- w.JobChannel 43 | select { 44 | case job := <-w.JobChannel: 45 | fmt.Printf("Worker %d received job %d\n", w.ID, job.ID) 46 | wg.Done() 47 | case <-w.quit: 48 | return 49 | } 50 | } 51 | }() 52 | } 53 | 54 | func (w *Worker) Stop() { 55 | go func() { 56 | w.quit <- true 57 | }() 58 | } 59 | ``` 60 | 61 | `Job` is a simple structure with just an ID. It represents a task that needs to be done by a worker. 62 | 63 | ```go 64 | type Job struct { 65 | ID int 66 | } 67 | ``` 68 | 69 | The singleton `WorkerPool` is initialized using `GetWorkerPool`, which ensures the singleton nature using `sync.Once`. Inside `GetWorkerPool`, a number of workers are started equal to `maxWorkers`. A dispatch function is also started that continually listens for incoming jobs on the jobs channel of the `WorkerPool`, and assigns each job to a worker. The `AddJob` method increases the `WaitGroup` counter and sends the job into the `jobQueue`. The `dispatch` method pulls jobs from `jobQueue` and sends them to available workers, ensuring that jobs are distributed to workers as they become available. The `Wait` method of the `WorkerPool` waits for all jobs to finish. In the main function, we call this method after all jobs have been added to ensure that the program doesn't exit until all jobs have been processed. 70 | 71 | ```go 72 | func GetWorkerPool(maxWorkers int) *WorkerPool { 73 | once.Do(func() { 74 | workers := make([]*Worker, maxWorkers) 75 | workerPool := make(chan chan Job, maxWorkers) 76 | jobQueue := make(chan Job, maxWorkers) 77 | 78 | pool := &WorkerPool{ 79 | workers: workers, 80 | jobQueue: jobQueue, 81 | workerPool: workerPool, 82 | } 83 | 84 | for i := 0; i < maxWorkers; i++ { 85 | worker := NewWorker(pool.workerPool, i) 86 | worker.Start(&pool.wg) 87 | workers[i] = worker 88 | } 89 | 90 | go pool.dispatch() 91 | 92 | singleton = pool 93 | }) 94 | 95 | return singleton 96 | } 97 | 98 | func (wp *WorkerPool) dispatch() { 99 | for job := range wp.jobQueue { 100 | workerJobQueue := <-wp.workerPool 101 | workerJobQueue <- job 102 | } 103 | } 104 | 105 | func (wp *WorkerPool) AddJob(job Job) { 106 | wp.wg.Add(1) 107 | wp.jobQueue <- job 108 | } 109 | 110 | func (wp *WorkerPool) Wait() { 111 | wp.wg.Wait() 112 | } 113 | ``` 114 | 115 | This code will start 5 workers and process 20 jobs. Each job will be picked up by an available worker and processed concurrently. The main function will wait for all jobs to be processed before exiting. 116 | 117 | ```go 118 | func main() { 119 | wp := GetWorkerPool(5) 120 | 121 | for i := 1; i <= 20; i++ { 122 | job := Job{ID: i} 123 | wp.AddJob(job) 124 | } 125 | 126 | wp.Wait() 127 | } 128 | ``` 129 | -------------------------------------------------------------------------------- /creational/singleton/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | "sync" 6 | ) 7 | 8 | type Job struct { 9 | ID int 10 | } 11 | 12 | type Worker struct { 13 | ID int 14 | WorkerPool chan chan Job 15 | JobChannel chan Job 16 | quit chan bool 17 | } 18 | 19 | type WorkerPool struct { 20 | workers []*Worker 21 | jobQueue chan Job 22 | workerPool chan chan Job 23 | wg sync.WaitGroup 24 | } 25 | 26 | var once sync.Once 27 | var singleton *WorkerPool 28 | 29 | func NewWorker(workerPool chan chan Job, id int) *Worker { 30 | return &Worker{ 31 | ID: id, 32 | WorkerPool: workerPool, 33 | JobChannel: make(chan Job), 34 | quit: make(chan bool), 35 | } 36 | } 37 | 38 | func (w *Worker) Start(wg *sync.WaitGroup) { 39 | go func() { 40 | for { 41 | w.WorkerPool <- w.JobChannel 42 | select { 43 | case job := <-w.JobChannel: 44 | fmt.Printf("Worker %d received job %d\n", w.ID, job.ID) 45 | wg.Done() 46 | case <-w.quit: 47 | return 48 | } 49 | } 50 | }() 51 | } 52 | 53 | func (w *Worker) Stop() { 54 | go func() { 55 | w.quit <- true 56 | }() 57 | } 58 | 59 | func GetWorkerPool(maxWorkers int) *WorkerPool { 60 | once.Do(func() { 61 | workers := make([]*Worker, maxWorkers) 62 | workerPool := make(chan chan Job, maxWorkers) 63 | jobQueue := make(chan Job, maxWorkers) 64 | 65 | pool := &WorkerPool{ 66 | workers: workers, 67 | jobQueue: jobQueue, 68 | workerPool: workerPool, 69 | } 70 | 71 | for i := 0; i < maxWorkers; i++ { 72 | worker := NewWorker(pool.workerPool, i) 73 | worker.Start(&pool.wg) 74 | workers[i] = worker 75 | } 76 | 77 | go pool.dispatch() 78 | 79 | singleton = pool 80 | }) 81 | 82 | return singleton 83 | } 84 | 85 | func (wp *WorkerPool) dispatch() { 86 | for job := range wp.jobQueue { 87 | workerJobQueue := <-wp.workerPool 88 | workerJobQueue <- job 89 | } 90 | } 91 | 92 | func (wp *WorkerPool) AddJob(job Job) { 93 | wp.wg.Add(1) 94 | wp.jobQueue <- job 95 | } 96 | 97 | func (wp *WorkerPool) Wait() { 98 | wp.wg.Wait() 99 | } 100 | 101 | func main() { 102 | wp := GetWorkerPool(5) 103 | 104 | for i := 1; i <= 20; i++ { 105 | job := Job{ID: i} 106 | wp.AddJob(job) 107 | } 108 | 109 | wp.Wait() 110 | } 111 | -------------------------------------------------------------------------------- /go.mod: -------------------------------------------------------------------------------- 1 | module github.com/araujo88/design-patterns-in-go/tree/main 2 | 3 | go 1.20 4 | -------------------------------------------------------------------------------- /go.sum: -------------------------------------------------------------------------------- https://raw.githubusercontent.com/leo-aa88/design-patterns-in-go/b1ecfd29985e22835f643d46053069082e90edb4/go.sum -------------------------------------------------------------------------------- /other/data_access_object/README.md: -------------------------------------------------------------------------------- 1 | # Data Access Object (DAO) 2 | 3 | A Data Access Object (DAO) is a pattern used in software design to separate the logic that retrieves data from a database from the business logic of the application. Essentially, it creates an abstraction over the data source, which can be a database or an API or anything else where data is retrieved. The DAO interacts with the data source and provides an interface that the rest of the application can use, without having to know any details about how the data is stored or retrieved. 4 | 5 | This pattern is widely used because it allows the underlying data source to be changed without affecting the rest of the application. This means that if you decide to change from one database system to another, you would only have to modify the DAO layer and not the entire application. 6 | 7 | ## Example 8 | 9 | Here's a simple example of a DAO pattern in Go, working with a fictional user database. 10 | 11 | First, let's define the User struct and the DAO interface: 12 | 13 | ```go 14 | type User struct { 15 | ID int 16 | FirstName string 17 | LastName string 18 | } 19 | 20 | type UserDAO interface { 21 | GetUser(id int) (*User, error) 22 | GetAllUsers() ([]*User, error) 23 | SaveUser(user *User) error 24 | DeleteUser(id int) error 25 | } 26 | ``` 27 | 28 | Now let's create a concrete implementation of this DAO interface. For simplicity, I'll use a mock in-memory database: 29 | 30 | ```go 31 | type UserDAOImpl struct { 32 | users map[int]*User 33 | } 34 | 35 | func (dao *UserDAOImpl) GetUser(id int) (*User, error) { 36 | user, exists := dao.users[id] 37 | if !exists { 38 | return nil, fmt.Errorf("User not found") 39 | } 40 | return user, nil 41 | } 42 | 43 | func (dao *UserDAOImpl) GetAllUsers() ([]*User, error) { 44 | userList := make([]*User, 0, len(dao.users)) 45 | for _, user := range dao.users { 46 | userList = append(userList, user) 47 | } 48 | return userList, nil 49 | } 50 | 51 | func (dao *UserDAOImpl) SaveUser(user *User) error { 52 | dao.users[user.ID] = user 53 | return nil 54 | } 55 | 56 | func (dao *UserDAOImpl) DeleteUser(id int) error { 57 | _, exists := dao.users[id] 58 | if !exists { 59 | return fmt.Errorf("User not found") 60 | } 61 | delete(dao.users, id) 62 | return nil 63 | } 64 | ``` 65 | 66 | Create a Service that Depends on the `UserDAO` Interface: 67 | 68 | ```go 69 | type UserService struct { 70 | userDao UserDAO 71 | } 72 | 73 | func NewUserService(dao UserDAO) *UserService { 74 | return &UserService{userDao: dao} 75 | } 76 | 77 | func (s *UserService) GetUserDetails(id int) (*User, error) { 78 | return s.userDao.GetUser(id) 79 | } 80 | ``` 81 | 82 | Use the Service in the Main Function: 83 | 84 | ```go 85 | func main() { 86 | userDao := &UserDAOImpl{ 87 | users: make(map[int]*User), 88 | } 89 | userService := NewUserService(userDao) 90 | 91 | user := &User{ 92 | ID: 1, 93 | FirstName: "Giga", 94 | LastName: "Chad", 95 | } 96 | userDao.SaveUser(user) 97 | 98 | retrievedUser, err := userService.GetUserDetails(1) 99 | if err != nil { 100 | log.Fatal(err) 101 | } 102 | fmt.Println("Retrieved User:", retrievedUser.FirstName, retrievedUser.LastName) 103 | } 104 | ``` 105 | 106 | Here, the `UserService` depends on the `UserDAO` interface, not the concrete `UserDAOImpl`. This way, if you decide to change how users are stored (e.g., switching from an in-memory database to a SQL database), you can create a new implementation of the `UserDAO` interface without changing the `UserService`. 107 | 108 | This example illustrates the DAO pattern's decoupling concept. By relying on interfaces, different parts of the application can interact without knowing the underlying implementation details, leading to more maintainable and flexible code. 109 | -------------------------------------------------------------------------------- /other/data_access_object/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | "log" 6 | ) 7 | 8 | type User struct { 9 | ID int 10 | FirstName string 11 | LastName string 12 | } 13 | 14 | type UserDAO interface { 15 | GetUser(id int) (*User, error) 16 | GetAllUsers() ([]*User, error) 17 | SaveUser(user *User) error 18 | DeleteUser(id int) error 19 | } 20 | 21 | type UserDAOImpl struct { 22 | users map[int]*User 23 | } 24 | 25 | func (dao *UserDAOImpl) GetUser(id int) (*User, error) { 26 | user, exists := dao.users[id] 27 | if !exists { 28 | return nil, fmt.Errorf("User not found") 29 | } 30 | return user, nil 31 | } 32 | 33 | func (dao *UserDAOImpl) GetAllUsers() ([]*User, error) { 34 | userList := make([]*User, 0, len(dao.users)) 35 | for _, user := range dao.users { 36 | userList = append(userList, user) 37 | } 38 | return userList, nil 39 | } 40 | 41 | func (dao *UserDAOImpl) SaveUser(user *User) error { 42 | dao.users[user.ID] = user 43 | return nil 44 | } 45 | 46 | func (dao *UserDAOImpl) DeleteUser(id int) error { 47 | _, exists := dao.users[id] 48 | if !exists { 49 | return fmt.Errorf("User not found") 50 | } 51 | delete(dao.users, id) 52 | return nil 53 | } 54 | 55 | type UserService struct { 56 | userDao UserDAO 57 | } 58 | 59 | func NewUserService(dao UserDAO) *UserService { 60 | return &UserService{userDao: dao} 61 | } 62 | 63 | func (s *UserService) GetUserDetails(id int) (*User, error) { 64 | return s.userDao.GetUser(id) 65 | } 66 | 67 | func main() { 68 | userDao := &UserDAOImpl{ 69 | users: make(map[int]*User), 70 | } 71 | userService := NewUserService(userDao) 72 | 73 | user := &User{ 74 | ID: 1, 75 | FirstName: "Giga", 76 | LastName: "Chad", 77 | } 78 | userDao.SaveUser(user) 79 | 80 | retrievedUser, err := userService.GetUserDetails(1) 81 | if err != nil { 82 | log.Fatal(err) 83 | } 84 | fmt.Println("Retrieved User:", retrievedUser.FirstName, retrievedUser.LastName) 85 | } 86 | -------------------------------------------------------------------------------- /other/dependency_injection/README.md: -------------------------------------------------------------------------------- 1 | # Dependency Injection 2 | 3 | Dependency Injection is a design pattern that allows the removal of hard-coded dependencies and makes it possible to change them, whether at run-time or compile-time. This pattern is particularly useful for decoupling components and improving code maintainability and testability. 4 | 5 | In simple terms, Dependency Injection means that if a class needs access to an external resource (like a database, or another class), instead of creating it inside the class, you "inject" it into the class from the outside. 6 | 7 | ### Participants 8 | 9 | - **Client**: The class that depends on the service. 10 | - **Service**: The service that the client needs. 11 | - **Injector**: This class injects the service into the client. 12 | 13 | ## Example 14 | 15 | Below is a simplified example in Go that demonstrates Dependency Injection. We have an `Author` struct that uses an interface `Writer` to write something. We then have two implementations of `Writer`: `ConsoleWriter` and `FileWriter`. Through dependency injection, we can easily switch between writing to the console and writing to a file without modifying the `Author` struct. 16 | 17 | ```go 18 | // Writer interface, the 'Service' in our example 19 | type Writer interface { 20 | Write([]byte) error 21 | } 22 | 23 | // ConsoleWriter writes to the console, one of the 'ConcreteService' 24 | type ConsoleWriter struct{} 25 | 26 | func (cw *ConsoleWriter) Write(data []byte) error { 27 | _, err := fmt.Println(string(data)) 28 | return err 29 | } 30 | 31 | // FileWriter writes to a file, another 'ConcreteService' 32 | type FileWriter struct { 33 | filename string 34 | } 35 | 36 | func (fw *FileWriter) Write(data []byte) error { 37 | return ioutil.WriteFile(fw.filename, data, 0644) 38 | } 39 | 40 | // Author is the 'Client' 41 | type Author struct { 42 | writer Writer // Author depends on a Writer to do the writing 43 | } 44 | 45 | // NewAuthor creates a new author with a writer 46 | func NewAuthor(writer Writer) *Author { 47 | return &Author{writer} 48 | } 49 | 50 | // WriteArticle uses the injected writer to write an article 51 | func (a *Author) WriteArticle(article string) error { 52 | return a.writer.Write([]byte(article)) 53 | } 54 | ``` 55 | 56 | In this example: 57 | 58 | - `Writer` is the service interface that defines a `Write` method. 59 | - `ConsoleWriter` and `FileWriter` are concrete implementations of the `Writer` interface. 60 | - `Author` is the client that depends on a service implementing the `Writer` interface. 61 | 62 | We inject the `Writer` dependency into `Author` via the `NewAuthor` function. This decouples `Author` from the concrete implementations (`ConsoleWriter` and `FileWriter`) and makes the system easier to extend, test, and maintain. 63 | 64 | With Dependency Injection, you can easily swap out the `Writer` implementation without modifying the `Author` code, making the system more modular and easier to test. 65 | -------------------------------------------------------------------------------- /other/dependency_injection/article.txt: -------------------------------------------------------------------------------- 1 | Article to file -------------------------------------------------------------------------------- /other/dependency_injection/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | "io/ioutil" 6 | ) 7 | 8 | // Writer interface, the 'Service' in our example 9 | type Writer interface { 10 | Write([]byte) error 11 | } 12 | 13 | // ConsoleWriter writes to the console, one of the 'ConcreteService' 14 | type ConsoleWriter struct{} 15 | 16 | func (cw *ConsoleWriter) Write(data []byte) error { 17 | _, err := fmt.Println(string(data)) 18 | return err 19 | } 20 | 21 | // FileWriter writes to a file, another 'ConcreteService' 22 | type FileWriter struct { 23 | filename string 24 | } 25 | 26 | func (fw *FileWriter) Write(data []byte) error { 27 | return ioutil.WriteFile(fw.filename, data, 0644) 28 | } 29 | 30 | // Author is the 'Client' 31 | type Author struct { 32 | writer Writer // Author depends on a Writer to do the writing 33 | } 34 | 35 | // NewAuthor creates a new author with a writer 36 | func NewAuthor(writer Writer) *Author { 37 | return &Author{writer} 38 | } 39 | 40 | // WriteArticle uses the injected writer to write an article 41 | func (a *Author) WriteArticle(article string) error { 42 | return a.writer.Write([]byte(article)) 43 | } 44 | 45 | func main() { 46 | // Inject ConsoleWriter dependency into Author 47 | author1 := NewAuthor(&ConsoleWriter{}) 48 | _ = author1.WriteArticle("Article to console") 49 | 50 | // Inject FileWriter dependency into Author 51 | author2 := NewAuthor(&FileWriter{filename: "article.txt"}) 52 | _ = author2.WriteArticle("Article to file") 53 | } 54 | -------------------------------------------------------------------------------- /other/repository/README.md: -------------------------------------------------------------------------------- 1 | # Repository 2 | 3 | The Repository pattern is a structural pattern used to separate the logic that retrieves data from a database (or any other source) from the business logic of the application. The Repository mediates between the application’s business logic and data source, acting like an in-memory collection of domain objects. Clients interact with a Repository as they would interact with a simple collection of objects, using methods like `Add`, `Remove`, and `Find`. 4 | 5 | ### Benefits 6 | 7 | 1. **Separation of Concerns**: It separates the logic of data access from the business logic. 8 | 2. **Testability**: Because the data logic is decoupled, it's easier to write unit tests for the business logic. 9 | 3. **Maintainability**: The code is more maintainable and readable, as each part follows the Single Responsibility Principle. 10 | 11 | ## Example 12 | 13 | Below is an example in Go that uses the Repository pattern. It demonstrates a simple CRUD operation for managing books in a library. 14 | 15 | ```go 16 | // Book represents a book in a library 17 | type Book struct { 18 | ID string 19 | Title string 20 | Author string 21 | } 22 | 23 | // BookRepository interface for persisting books 24 | type BookRepository interface { 25 | Add(Book) error 26 | Remove(string) error 27 | FindById(string) (*Book, error) 28 | FindAll() ([]*Book, error) 29 | } 30 | 31 | // InMemoryBookRepository is an in-memory implementation of BookRepository 32 | type InMemoryBookRepository struct { 33 | books map[string]*Book 34 | } 35 | 36 | // NewInMemoryBookRepository initializes a new InMemoryBookRepository 37 | func NewInMemoryBookRepository() *InMemoryBookRepository { 38 | return &InMemoryBookRepository{ 39 | books: make(map[string]*Book), 40 | } 41 | } 42 | 43 | func (r *InMemoryBookRepository) Add(b Book) error { 44 | r.books[b.ID] = &b 45 | return nil 46 | } 47 | 48 | func (r *InMemoryBookRepository) Remove(id string) error { 49 | delete(r.books, id) 50 | return nil 51 | } 52 | 53 | func (r *InMemoryBookRepository) FindById(id string) (*Book, error) { 54 | if book, ok := r.books[id]; ok { 55 | return book, nil 56 | } 57 | return nil, fmt.Errorf("Book not found") 58 | } 59 | 60 | func (r *InMemoryBookRepository) FindAll() ([]*Book, error) { 61 | var books []*Book 62 | for _, book := range r.books { 63 | books = append(books, book) 64 | } 65 | return books, nil 66 | } 67 | ``` 68 | 69 | In this example: 70 | 71 | - `Book` is the domain object. 72 | - `BookRepository` is the interface that defines methods for accessing `Book` objects. 73 | - `InMemoryBookRepository` is the concrete implementation of the `BookRepository`, which stores `Book` objects in an in-memory map. 74 | 75 | This separation makes it easier to change the data source or implement additional features like caching. It also simplifies testing, as you can easily mock the `BookRepository` when testing components that rely on it. 76 | 77 | ## Differences between DAO and Repository patterns 78 | 79 | Both the Repository and Data Access Object (DAO) patterns aim to separate the concerns of data access from the rest of the application, but they differ in scope, abstraction level, and how they are used in the context of an application. Here are some key differences: 80 | 81 | ### Abstraction Level 82 | 83 | - **Repository Pattern**: Provides a higher level of abstraction by dealing with domain objects and collections of domain objects. A repository typically works with aggregates in terms of Domain-Driven Design (DDD) and operates in the context of the business domain, effectively decoupling the domain model from the data model. 84 | 85 | - **DAO Pattern**: Focuses on providing a low-level abstraction over the database interactions. It directly deals with data source APIs and is generally closer to the database, often reflecting the database's structure, tables, or stored procedures. 86 | 87 | ### Operations 88 | 89 | - **Repository Pattern**: Methods in repositories often have a business-centric language. For example, you may have methods like `FindActiveUsers` or `GetOverdueAccounts`, which represent specific business rules. 90 | 91 | - **DAO Pattern**: Methods in a DAO are usually CRUD-oriented (Create, Read, Update, Delete) and closely represent the operations you can perform on the table itself. You might find methods like `Insert`, `Update`, `Delete`, `FindById`, etc. 92 | 93 | ### Aggregation 94 | 95 | - **Repository Pattern**: Typically deals with aggregates, which are cluster of domain objects that can be treated as a single unit, and often returns fully instantiated aggregates that are ready for use by the client code. 96 | 97 | - **DAO Pattern**: Generally works with individual records in tables and doesn't concern itself with object graphs or aggregates. 98 | 99 | ### Usage Context 100 | 101 | - **Repository Pattern**: Commonly used in Domain-Driven Design and places an emphasis on business rules and the domain. It's often used in more complex applications where business logic needs to be decoupled from data access logic. 102 | 103 | - **DAO Pattern**: More general-purpose and can be used effectively in simpler, CRUD-based applications or any application that doesn't place much emphasis on domain-driven design. 104 | 105 | ### Interface Location 106 | 107 | - **Repository Pattern**: Usually defined in the domain layer and is meant to be an abstraction of a collection of domain objects. 108 | 109 | - **DAO Pattern**: Defined in the data access layer and serves as an abstraction for database operations. 110 | 111 | ### Testability 112 | 113 | - Both patterns aim to improve testability by separating data access concerns from business logic, but the Repository pattern often goes a step further by working well with domain-centric unit tests, given its higher level of abstraction. 114 | 115 | While both patterns aim to achieve similar separation of concerns, the way they go about it and their typical usages are different. Sometimes, you might even use both in the same application: DAOs can be used to handle the low-level data access details, while repositories use DAOs internally to implement the higher-level, domain-specific data access interfaces. 116 | -------------------------------------------------------------------------------- /other/repository/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | // Book represents a book in a library 6 | type Book struct { 7 | ID string 8 | Title string 9 | Author string 10 | } 11 | 12 | // BookRepository interface for persisting books 13 | type BookRepository interface { 14 | Add(Book) error 15 | Remove(string) error 16 | FindById(string) (*Book, error) 17 | FindAll() ([]*Book, error) 18 | } 19 | 20 | // InMemoryBookRepository is an in-memory implementation of BookRepository 21 | type InMemoryBookRepository struct { 22 | books map[string]*Book 23 | } 24 | 25 | // NewInMemoryBookRepository initializes a new InMemoryBookRepository 26 | func NewInMemoryBookRepository() *InMemoryBookRepository { 27 | return &InMemoryBookRepository{ 28 | books: make(map[string]*Book), 29 | } 30 | } 31 | 32 | func (r *InMemoryBookRepository) Add(b Book) error { 33 | r.books[b.ID] = &b 34 | return nil 35 | } 36 | 37 | func (r *InMemoryBookRepository) Remove(id string) error { 38 | delete(r.books, id) 39 | return nil 40 | } 41 | 42 | func (r *InMemoryBookRepository) FindById(id string) (*Book, error) { 43 | if book, ok := r.books[id]; ok { 44 | return book, nil 45 | } 46 | return nil, fmt.Errorf("Book not found") 47 | } 48 | 49 | func (r *InMemoryBookRepository) FindAll() ([]*Book, error) { 50 | var books []*Book 51 | for _, book := range r.books { 52 | books = append(books, book) 53 | } 54 | return books, nil 55 | } 56 | 57 | func main() { 58 | repo := NewInMemoryBookRepository() 59 | 60 | // Add books 61 | repo.Add(Book{ID: "1", Title: "1984", Author: "George Orwell"}) 62 | repo.Add(Book{ID: "2", Title: "Brave New World", Author: "Aldous Huxley"}) 63 | 64 | // Find a book by ID 65 | book, err := repo.FindById("1") 66 | if err != nil { 67 | fmt.Println("Error:", err) 68 | } else { 69 | fmt.Println("Found book:", *book) 70 | } 71 | 72 | // Find all books 73 | allBooks, err := repo.FindAll() 74 | if err != nil { 75 | fmt.Println("Error:", err) 76 | } else { 77 | for _, book := range allBooks { 78 | fmt.Println(*book) 79 | } 80 | } 81 | 82 | // Remove a book 83 | err = repo.Remove("1") 84 | if err != nil { 85 | fmt.Println("Error:", err) 86 | } 87 | 88 | // Try to find the removed book 89 | book, err = repo.FindById("1") 90 | if err != nil { 91 | fmt.Println("Error:", err) 92 | } else { 93 | fmt.Println("Found book:", *book) 94 | } 95 | } 96 | -------------------------------------------------------------------------------- /other/service_locator/README.md: -------------------------------------------------------------------------------- 1 | # Service locator 2 | 3 | The Service Locator pattern is a design pattern used in software development to encapsulate the processes involved in obtaining a service with a strong abstraction layer. This pattern uses a central registry known as the "service locator", which on request returns the information necessary to perform a certain task. 4 | 5 | Here is a brief summary of the pattern: 6 | 7 | - The service locator is a known point for obtaining services. 8 | - The service locator may 'know' how to get hold of the service itself, or it might contain a record of suitable services (i.e., a registry). 9 | - An application will ask the service locator for the service by passing a string identifier or a key. 10 | - The locator will return the service to the application so that the application can use it. 11 | 12 | This pattern introduces an abstraction layer between the service consumer and the concrete classes providing those services. This abstraction layer provides a way to manage dependencies and to do runtime binding of the required service. 13 | 14 | ## Example 15 | 16 | The Service Locator pattern is commonly used in situations where program configuration dictates what services to use. This pattern is particularly popular in microservice architectures and large enterprise systems, where services might be spread across different servers or even geographic regions. 17 | 18 | The following example uses a service locator to switch between different databases (PostgreSQL and MySQL). We'll create a generic `DatabaseService` interface, and two structs implementing it, one for each database. 19 | 20 | ```go 21 | // Define our Service Interface 22 | type DatabaseService interface { 23 | GetName() string 24 | Connect() string 25 | } 26 | 27 | type PostgreSQL struct{} 28 | 29 | func (p *PostgreSQL) GetName() string { 30 | return "PostgreSQL" 31 | } 32 | 33 | func (p *PostgreSQL) Connect() string { 34 | return "Connected to PostgreSQL" 35 | } 36 | 37 | type MySQL struct{} 38 | 39 | func (m *MySQL) GetName() string { 40 | return "MySQL" 41 | } 42 | 43 | func (m *MySQL) Connect() string { 44 | return "Connected to MySQL" 45 | } 46 | 47 | // Service Locator 48 | type DatabaseServiceLocator struct { 49 | services map[string]DatabaseService 50 | } 51 | 52 | func (sl *DatabaseServiceLocator) GetService(serviceName string) (DatabaseService, error) { 53 | service, ok := sl.services[serviceName] 54 | if ok { 55 | return service, nil 56 | } 57 | return nil, fmt.Errorf("Service Not Found") 58 | } 59 | 60 | func (sl *DatabaseServiceLocator) RegisterService(service DatabaseService) { 61 | sl.services[service.GetName()] = service 62 | } 63 | ``` 64 | 65 | In this example, we have defined a common interface (`DatabaseService`) for our databases and implemented it for PostgreSQL and MySQL. The `DatabaseServiceLocator` is our service locator which maintains a registry of services. We can fetch a specific database service by its name, and then call Connect() to simulate establishing a connection to the database. 66 | 67 | We use the service locator in our main() function to fetch and connect to our databases. The type of database we're connecting to could be configured based on external factors, like application configuration or environment variables, making the system highly flexible. 68 | -------------------------------------------------------------------------------- /other/service_locator/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | "log" 6 | ) 7 | 8 | // Define our Service Interface 9 | type DatabaseService interface { 10 | GetName() string 11 | Connect() string 12 | } 13 | 14 | type PostgreSQL struct{} 15 | 16 | func (p *PostgreSQL) GetName() string { 17 | return "PostgreSQL" 18 | } 19 | 20 | func (p *PostgreSQL) Connect() string { 21 | return "Connected to PostgreSQL" 22 | } 23 | 24 | type MySQL struct{} 25 | 26 | func (m *MySQL) GetName() string { 27 | return "MySQL" 28 | } 29 | 30 | func (m *MySQL) Connect() string { 31 | return "Connected to MySQL" 32 | } 33 | 34 | // Service Locator 35 | type DatabaseServiceLocator struct { 36 | services map[string]DatabaseService 37 | } 38 | 39 | func (sl *DatabaseServiceLocator) GetService(serviceName string) (DatabaseService, error) { 40 | service, ok := sl.services[serviceName] 41 | if ok { 42 | return service, nil 43 | } 44 | return nil, fmt.Errorf("Service Not Found") 45 | } 46 | 47 | func (sl *DatabaseServiceLocator) RegisterService(service DatabaseService) { 48 | sl.services[service.GetName()] = service 49 | } 50 | 51 | func main() { 52 | locator := &DatabaseServiceLocator{ 53 | services: make(map[string]DatabaseService), 54 | } 55 | 56 | postgres := &PostgreSQL{} 57 | locator.RegisterService(postgres) 58 | 59 | mysql := &MySQL{} 60 | locator.RegisterService(mysql) 61 | 62 | // Fetch PostgreSQL service and connect 63 | service, err := locator.GetService("PostgreSQL") 64 | if err != nil { 65 | log.Fatal(err) 66 | } 67 | fmt.Println(service.Connect()) 68 | 69 | // Fetch MySQL service and connect 70 | service, err = locator.GetService("MySQL") 71 | if err != nil { 72 | log.Fatal(err) 73 | } 74 | fmt.Println(service.Connect()) 75 | } 76 | -------------------------------------------------------------------------------- /structural/adapter/README.md: -------------------------------------------------------------------------------- 1 | # Adapter 2 | 3 | The Adapter Design Pattern is a structural design pattern that allows two incompatible interfaces to work together. This incompatibility could be because of differences in method names, argument types, or other differences in the interfaces. 4 | 5 | The Adapter acts as a wrapper between two objects. It catches calls for one object and transforms them to format and interface recognizable by the second object. 6 | 7 | Here's an example: Suppose you have a legacy system that returns data in an older format (like XML), and you have a new system that expects the data to be in a different format (like JSON). Instead of rewriting the legacy system, you could use an Adapter. This Adapter could take the XML data, convert it to JSON, and then provide the data to the new system. 8 | 9 | In a real-world scenario, an adapter is like having a USB-C to USB-A converter. You have a device that only supports USB-C as an input but you have a USB-A connector cable. So you use a converter/adapter to solve the incompatibility. 10 | 11 | The Adapter Design Pattern is all about creating an intermediary abstraction that translates, or adapts, the old component to the new system. An adapter wraps the legacy system with a new interface so that the legacy system can be used by the new system through the new interface. This way, the new system only interacts with the Adapter but the legacy system doesn't need to be modified. 12 | 13 | ## Example 14 | 15 | Imagine we have a legacy system that logs messages in a certain way and a new system that has a different interface for logging. 16 | 17 | The legacy system has a `LegacyLogger` with a `LogMessage` method: 18 | 19 | ```go 20 | type LegacyLogger struct {} 21 | 22 | func (l *LegacyLogger) LogMessage(message string) { 23 | fmt.Println("Legacy logger: " + message) 24 | } 25 | ``` 26 | 27 | The new system uses an interface called `NewLogger` with a `Log` method: 28 | 29 | ```go 30 | type NewLogger interface { 31 | Log(message string) 32 | } 33 | 34 | type NewSystemLogger struct {} 35 | 36 | func (l *NewSystemLogger) Log(message string) { 37 | fmt.Println("New system logger: " + message) 38 | } 39 | ``` 40 | 41 | You want the new system to be able to use the `LegacyLogger` without changing its code. You can create an adapter that implements the `NewLogger` interface, but uses the `LegacyLogger` internally: 42 | 43 | ```go 44 | type LoggerAdapter struct { 45 | legacyLogger *LegacyLogger 46 | } 47 | 48 | func (a *LoggerAdapter) Log(message string) { 49 | // Adapting the interface here: 50 | a.legacyLogger.LogMessage(message) 51 | } 52 | ``` 53 | 54 | Now, you can use `LegacyLogger` in the new system: 55 | 56 | ```go 57 | func logMessage(message string, logger NewLogger) { 58 | logger.Log(message) 59 | } 60 | 61 | func main() { 62 | legacyLogger := &LegacyLogger{} 63 | loggerAdapter := &LoggerAdapter{legacyLogger: legacyLogger} 64 | 65 | logMessage("Hello, world!", loggerAdapter) 66 | } 67 | ``` 68 | 69 | In this example, `LoggerAdapter` is the adapter. It wraps `LegacyLogger` (the adaptee) and makes it compatible with `NewLogger` (the target interface). The `Log` method in `LoggerAdapter` adapts the interface of `LegacyLogger` to the `NewLogger` interface. The client code (the `logMessage` function) works with the `NewLogger` interface, so it can now use `LegacyLogger` through the `LoggerAdapter`. This is the essence of the Adapter Pattern. 70 | -------------------------------------------------------------------------------- /structural/adapter/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | type LegacyLogger struct{} 6 | 7 | func (l *LegacyLogger) LogMessage(message string) { 8 | fmt.Println("Legacy logger: " + message) 9 | } 10 | 11 | type NewLogger interface { 12 | Log(message string) 13 | } 14 | 15 | type NewSystemLogger struct{} 16 | 17 | func (l *NewSystemLogger) Log(message string) { 18 | fmt.Println("New system logger: " + message) 19 | } 20 | 21 | type LoggerAdapter struct { 22 | legacyLogger *LegacyLogger 23 | } 24 | 25 | func (a *LoggerAdapter) Log(message string) { 26 | // Adapting the interface here: 27 | a.legacyLogger.LogMessage(message) 28 | } 29 | 30 | func logMessage(message string, logger NewLogger) { 31 | logger.Log(message) 32 | } 33 | 34 | func main() { 35 | legacyLogger := &LegacyLogger{} 36 | loggerAdapter := &LoggerAdapter{legacyLogger: legacyLogger} 37 | newLogger := &NewSystemLogger{} 38 | 39 | logMessage("Hello, world!", loggerAdapter) 40 | logMessage("Hello, world!", newLogger) 41 | } 42 | -------------------------------------------------------------------------------- /structural/bridge/README.md: -------------------------------------------------------------------------------- 1 | # Bridge 2 | 3 | The Bridge Design Pattern is a structural design pattern that aims to decouple an abstraction from its implementation so that the two can vary independently. This is especially useful for providing platform independence and can also enhance extensibility. 4 | 5 | In other words, Bridge Pattern is about preferring composition over inheritance. Implementation details are pushed from a hierarchy to another object with a separate hierarchy. 6 | 7 | ## Example 8 | 9 | For example, consider different types of database drivers. We can have an interface called `DatabaseDriver` that has methods like `Connect()`, `ExecuteQuery()`, etc. Now, the actual implementations like `MySQLDriver`, `PostgresDriver`, `SQLiteDriver` will implement this `DatabaseDriver` interface and provide the actual implementation of these methods. So the abstraction layer (which could be an application using the database) will just call these methods and is not worried about what database system it is connecting to. This abstraction of implementation is the essence of the bridge pattern. 10 | 11 | ```go 12 | type IDatabase interface { 13 | Connect() string 14 | } 15 | 16 | type MySQL struct { 17 | } 18 | 19 | func (m MySQL) Connect() string { 20 | return "Connected to MySQL Database" 21 | } 22 | 23 | type Postgres struct { 24 | } 25 | 26 | func (p Postgres) Connect() string { 27 | return "Connected to Postgres Database" 28 | } 29 | 30 | type Application struct { 31 | database IDatabase 32 | } 33 | 34 | func (a *Application) SetDatabase(database IDatabase) { 35 | a.database = database 36 | } 37 | 38 | func (a *Application) Start() { 39 | fmt.Println(a.database.Connect()) 40 | } 41 | 42 | ``` 43 | 44 | In this example, we define an interface `IDatabase` that each of our specific database types (`MySQL`, `Postgres`) implements. This interface includes a method `Connect()`, which would be different for each database type. The `Application` struct then has a `SetDatabase()` method that accepts anything that fulfills the `IDatabase` interface. 45 | 46 | We then have a method `Start()` that prints the `Connect()` message. In a real-world application, it would contain the logic that is common to all databases. It could be interacting with the database, creating tables, performing CRUD operations, etc. 47 | 48 | By using the bridge pattern in this way, we're able to decouple the abstraction (our application's interaction with a database) from the implementation (the specific calls needed to interact with a MySQL or a PostgreSQL database). 49 | -------------------------------------------------------------------------------- /structural/bridge/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | type IDatabase interface { 6 | Connect() string 7 | } 8 | 9 | type MySQL struct { 10 | } 11 | 12 | func (m MySQL) Connect() string { 13 | return "Connected to MySQL Database" 14 | } 15 | 16 | type Postgres struct { 17 | } 18 | 19 | func (p Postgres) Connect() string { 20 | return "Connected to Postgres Database" 21 | } 22 | 23 | type Application struct { 24 | database IDatabase 25 | } 26 | 27 | func (a *Application) SetDatabase(database IDatabase) { 28 | a.database = database 29 | } 30 | 31 | func (a *Application) Start() { 32 | fmt.Println(a.database.Connect()) 33 | } 34 | 35 | func main() { 36 | mysql := &MySQL{} 37 | postgres := &Postgres{} 38 | 39 | app := &Application{} 40 | app.SetDatabase(mysql) 41 | app.Start() 42 | 43 | app.SetDatabase(postgres) 44 | app.Start() 45 | } 46 | -------------------------------------------------------------------------------- /structural/composite/README.md: -------------------------------------------------------------------------------- 1 | # Composite 2 | 3 | The Composite Design Pattern is a structural design pattern that allows you to compose objects into tree structures to represent part-whole hierarchies. The Composite pattern lets clients treat individual objects and compositions of objects uniformly. 4 | 5 | This pattern is used when we need to treat a group of objects in the same way as a single instance of an object. The intent of a composite is to "compose" objects into tree structures to represent part-whole hierarchies. Implementing the composite pattern lets clients treat individual objects and compositions uniformly. 6 | 7 | The composite pattern includes the following components: 8 | 9 | - Component: It is an interface for objects in the composition. It has methods to manage the child components. It can be an abstract class which contains default implementations. If there is no specific default implementations to put in the abstract class, it can also be an interface. 10 | 11 | - Leaf: It represents leaf objects in the composition. It has no children. 12 | 13 | - Composite: It stores the child components and implements the child related operations in the component interface. 14 | 15 | - Client: It manipulates objects in the composition through the component interface. 16 | 17 | A real-world example could be an organization hierarchy. Every employee of an organization is an object. The organization consists of departments and each department also has a list of employees. Here, each department can be seen as a composite object as it can be further divided into sub-departments. This way, the organization is the composition of employees and departments. This can be efficiently represented using the composite design pattern. 18 | 19 | ## Example 20 | 21 | Let's consider a file system as an example. In a file system, a directory can contain files or other directories. Here, both files and directories share similar operations such as calculating the size, searching for an item, etc. 22 | 23 | In this example, the Component can be an interface named `FileSystemNode`, the Leaf can be a `File` and the Composite can be a `Directory`. The `Directory` can contain both `File` and `Directory`. 24 | 25 | ```go 26 | // FileSystemNode : a component which can be a file or a directory 27 | type FileSystemNode interface { 28 | GetSize() int 29 | } 30 | 31 | // File : a leaf node in the file system 32 | type File struct { 33 | size int 34 | } 35 | 36 | // GetSize : returns size of the file 37 | func (f *File) GetSize() int { 38 | return f.size 39 | } 40 | 41 | // Directory : a composite node in the file system 42 | type Directory struct { 43 | children []FileSystemNode 44 | } 45 | 46 | // GetSize : returns total size of the directory (including all children) 47 | func (d *Directory) GetSize() int { 48 | size := 0 49 | for _, child := range d.children { 50 | size += child.GetSize() 51 | } 52 | return size 53 | } 54 | 55 | // AddChild : adds a new child node to the directory 56 | func (d *Directory) AddChild(child FileSystemNode) { 57 | d.children = append(d.children, child) 58 | } 59 | ``` 60 | 61 | In this example, the client (`main` function) treats all files and directories uniformly by using the `FileSystemNode` interface. The client doesn't need to be aware of the concrete object it's dealing with. This is the primary benefit of the Composite Design Pattern. 62 | -------------------------------------------------------------------------------- /structural/composite/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | // FileSystemNode : a component which can be a file or a directory 6 | type FileSystemNode interface { 7 | GetSize() int 8 | } 9 | 10 | // File : a leaf node in the file system 11 | type File struct { 12 | size int 13 | } 14 | 15 | // GetSize : returns size of the file 16 | func (f *File) GetSize() int { 17 | return f.size 18 | } 19 | 20 | // Directory : a composite node in the file system 21 | type Directory struct { 22 | children []FileSystemNode 23 | } 24 | 25 | // GetSize : returns total size of the directory (including all children) 26 | func (d *Directory) GetSize() int { 27 | size := 0 28 | for _, child := range d.children { 29 | size += child.GetSize() 30 | } 31 | return size 32 | } 33 | 34 | // AddChild : adds a new child node to the directory 35 | func (d *Directory) AddChild(child FileSystemNode) { 36 | d.children = append(d.children, child) 37 | } 38 | 39 | func main() { 40 | file1 := &File{size: 200} 41 | file2 := &File{size: 300} 42 | dir := Directory{} 43 | dir.AddChild(file1) 44 | dir.AddChild(file2) 45 | 46 | fmt.Println(dir.GetSize()) // Output: 500 47 | } 48 | -------------------------------------------------------------------------------- /structural/decorator/README.md: -------------------------------------------------------------------------------- 1 | # Decorator 2 | 3 | The Decorator design pattern allows us to add new functionalities to existing objects without altering their structures. This pattern involves a set of decorator classes that are used to wrap concrete components. Decorator classes mirror the type of the components they decorate but add or override behavior. 4 | 5 | The key feature of this pattern is the ability to "wrap" or "decorate" an object multiple times, with different decorators, adding cumulative behavior to the original object. The pattern is particularly useful for adding responsibilities to objects dynamically and optionally. 6 | 7 | Key Points: 8 | 9 | - Component Interface: This defines the interface for objects that can have responsibilities added to them dynamically. 10 | - Concrete Component: It is the object to which new responsibilities are added. 11 | - Decorator: This maintains a reference to a Component object and defines an interface that conforms to the Component's interface. 12 | - Concrete Decorators: These extend the Decorator and add specific responsibilities. 13 | 14 | ## Example 15 | 16 | Let's consider an example with input/output (I/O) operations in a system. Imagine you want to read data from a file. At its core, you just read raw bytes. But often you'll want to enhance this process with additional features such as: 17 | 18 | - Buffering: Read large chunks at once to improve performance. 19 | - Decompression: If your file is compressed, you might want to decompress it on-the-fly while reading. 20 | - Encryption: Maybe your data is encrypted, and you need to decrypt it when reading. 21 | 22 | Each of these features can be seen as a "decoration" to the basic file reading operation. Using the decorator pattern, you can dynamically construct a chain of operations for file reading. 23 | 24 | Here's an example in Go, focusing on the structure of the decorator pattern: 25 | 26 | ```go 27 | // Reader is our base component interface 28 | type Reader interface { 29 | Read() string 30 | } 31 | 32 | // FileReader reads from a file 33 | type FileReader struct{} 34 | 35 | func (fr *FileReader) Read() string { 36 | return "data from file" 37 | } 38 | 39 | // Buffered reader as a decorator 40 | type BufferedReader struct { 41 | reader Reader 42 | } 43 | 44 | func (br *BufferedReader) Read() string { 45 | data := br.reader.Read() 46 | return "buffered " + data 47 | } 48 | 49 | // Decrypt reader as another decorator 50 | type DecryptReader struct { 51 | reader Reader 52 | } 53 | 54 | func (dr *DecryptReader) Read() string { 55 | data := dr.reader.Read() 56 | return "decrypted " + data 57 | } 58 | ``` 59 | 60 | In this example: 61 | 62 | - `FileReader` provides basic file reading functionality. 63 | - `BufferedReader` and `DecryptReader` are decorators that extend the base reading functionality. 64 | 65 | By using the decorator pattern, we can stack or chain these operations in any combination we want, providing great flexibility. 66 | -------------------------------------------------------------------------------- /structural/decorator/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | ) 6 | 7 | // Reader is our base component interface 8 | type Reader interface { 9 | Read() string 10 | } 11 | 12 | // FileReader reads from a file 13 | type FileReader struct{} 14 | 15 | func (fr *FileReader) Read() string { 16 | return "data from file" 17 | } 18 | 19 | // Buffered reader as a decorator 20 | type BufferedReader struct { 21 | reader Reader 22 | } 23 | 24 | func (br *BufferedReader) Read() string { 25 | data := br.reader.Read() 26 | return "buffered " + data 27 | } 28 | 29 | // Decrypt reader as another decorator 30 | type DecryptReader struct { 31 | reader Reader 32 | } 33 | 34 | func (dr *DecryptReader) Read() string { 35 | data := dr.reader.Read() 36 | return "decrypted " + data 37 | } 38 | 39 | func main() { 40 | fileReader := &FileReader{} 41 | 42 | // Buffered read 43 | bufferedReader := &BufferedReader{reader: fileReader} 44 | fmt.Println(bufferedReader.Read()) 45 | 46 | // Buffered and decrypted read 47 | decryptBufferedReader := &DecryptReader{reader: bufferedReader} 48 | fmt.Println(decryptBufferedReader.Read()) 49 | } 50 | -------------------------------------------------------------------------------- /structural/facade/README.md: -------------------------------------------------------------------------------- 1 | # Façade 2 | 3 | The façade design pattern provides a unified interface to a set of interfaces in a subsystem. Façade defines a higher-level interface that makes the subsystem easier to use. Essentially, it simplifies a complex system by providing a single entry point to coordinate various functionalities. 4 | 5 | The main reasons to use the façade pattern are: 6 | 7 | - Simplification: It makes a complex system easier to understand and use by providing a simplified interface. 8 | - Decoupling: It decouples the subsystem from clients and other subsystems, promoting subsystem independence and portability. 9 | - Layering: You can use the façade to define an entry point to each subsystem level. This can be especially beneficial in layered architectures. 10 | 11 | The façade pattern can often be found in complex systems and frameworks to provide a simpler, more developer-friendly API. One common area in software engineering where the façade pattern is used is in the design of software libraries and frameworks. 12 | 13 | ## Example 14 | 15 | Let's say we're designing a library to interact with a database. Underneath the hood, connecting to a database might involve multiple steps: opening a connection, configuring connection parameters, setting up a session, etc. If you expose all these steps to the end developer, it can get cumbersome. 16 | 17 | Instead, you provide a simple façade that abstracts away the complexity. 18 | 19 | ```go 20 | // Complex library components 21 | type DatabaseConnection struct{} 22 | 23 | func (dc *DatabaseConnection) Open() { 24 | fmt.Println("Opening database connection...") 25 | } 26 | 27 | func (dc *DatabaseConnection) SetConfiguration() { 28 | fmt.Println("Setting configuration...") 29 | } 30 | 31 | type DatabaseSession struct{} 32 | 33 | func (ds *DatabaseSession) Init() { 34 | fmt.Println("Initializing session...") 35 | } 36 | 37 | // DatabaseFacade provides a simplified interface to interact with the database 38 | type DatabaseFacade struct { 39 | connection *DatabaseConnection 40 | session *DatabaseSession 41 | } 42 | 43 | func (df *DatabaseFacade) Start() { 44 | df.connection.Open() 45 | df.connection.SetConfiguration() 46 | df.session.Init() 47 | fmt.Println("Database started!") 48 | } 49 | ``` 50 | 51 | In the above example, the `DatabaseFacade` simplifies the operations needed to start a database session. The end developer using this library doesn't need to know about the intricacies of opening a connection, setting configurations, or initializing a session. They simply use the `Start()` method provided by the façade. 52 | 53 | In real-world software systems, the underlying components can be even more complex, and the façade would abstract away a lot more intricacies. This pattern helps in making the software more maintainable and reduces the learning curve for developers unfamiliar with all the details of the underlying subsystem. -------------------------------------------------------------------------------- /structural/facade/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import "fmt" 4 | 5 | // Complex library components 6 | type DatabaseConnection struct{} 7 | 8 | func (dc *DatabaseConnection) Open() { 9 | fmt.Println("Opening database connection...") 10 | } 11 | 12 | func (dc *DatabaseConnection) SetConfiguration() { 13 | fmt.Println("Setting configuration...") 14 | } 15 | 16 | type DatabaseSession struct{} 17 | 18 | func (ds *DatabaseSession) Init() { 19 | fmt.Println("Initializing session...") 20 | } 21 | 22 | // DatabaseFacade provides a simplified interface to interact with the database 23 | type DatabaseFacade struct { 24 | connection *DatabaseConnection 25 | session *DatabaseSession 26 | } 27 | 28 | func (df *DatabaseFacade) Start() { 29 | df.connection.Open() 30 | df.connection.SetConfiguration() 31 | df.session.Init() 32 | fmt.Println("Database started!") 33 | } 34 | 35 | func main() { 36 | // Using the façade to simplify the database operations 37 | dbFacade := &DatabaseFacade{ 38 | connection: &DatabaseConnection{}, 39 | session: &DatabaseSession{}, 40 | } 41 | dbFacade.Start() 42 | } 43 | -------------------------------------------------------------------------------- /structural/flyweight/README.md: -------------------------------------------------------------------------------- 1 | # Flyweight 2 | 3 | The Flyweight Design Pattern is a structural design pattern that provides a way to use objects in large numbers when a simple repeated representation would use an unacceptable amount of memory. 4 | 5 | Flyweight pattern introduces the concept of sharing common parts of the object state among multiple objects instead of keeping all of the data in each object. The object containing the shared state is usually called a "flyweight". The pattern allows programs to support vast quantities of objects by keeping their memory consumption low. 6 | 7 | A typical use case for the Flyweight pattern is a game, for example, where you have numerous objects (trees, buildings, NPCs, etc.) and you can't afford to expend your memory resources to store each object separately with all their properties. 8 | 9 | ## Example 10 | 11 | Let's consider a simple text formatting tool. This tool would need to format different ranges of text within a document with specific styles (bold, italic, underline, etc.). These styles are shared among multiple text ranges, and each text range could be considered a unique object. The Flyweight pattern would allow us to reuse style instances instead of duplicating them for each text range, therefore saving memory. 12 | 13 | ```go 14 | // TextStyle is a flyweight that represents a specific text style. 15 | type TextStyle struct { 16 | name string 17 | } 18 | 19 | // Format applies the text style to a text. 20 | func (t *TextStyle) Format(text string) string { 21 | return fmt.Sprintf("[%s %s]", t.name, text) 22 | } 23 | 24 | // TextStyleFactory creates and manages TextStyle instances. 25 | type TextStyleFactory struct { 26 | styles map[string]*TextStyle 27 | mu sync.Mutex 28 | } 29 | 30 | // GetTextStyle returns a TextStyle instance. It reuses an existing instance if available. 31 | func (f *TextStyleFactory) GetTextStyle(name string) *TextStyle { 32 | f.mu.Lock() 33 | defer f.mu.Unlock() 34 | 35 | if style, ok := f.styles[name]; ok { 36 | return style 37 | } 38 | 39 | style := &TextStyle{name: name} 40 | f.styles[name] = style 41 | return style 42 | } 43 | 44 | // TextRange represents a range of text within a document. 45 | type TextRange struct { 46 | Start, End int 47 | Text string 48 | Style *TextStyle 49 | } 50 | 51 | // NewTextRange creates a new text range. 52 | func NewTextRange(start, end int, text string, style *TextStyle) *TextRange { 53 | return &TextRange{ 54 | Start: start, 55 | End: end, 56 | Text: text, 57 | Style: style, 58 | } 59 | } 60 | 61 | // Format formats the text range with its text style. 62 | func (t *TextRange) Format() string { 63 | return t.Style.Format(t.Text) 64 | } 65 | ``` 66 | 67 | In this example, `TextStyle` is a flyweight that represents a text style. `TextStyleFactory` manages the creation and reuse of `TextStyle` instances. `TextRange` represents a range of text within a document and uses a `TextStyle` to format its text. By using the Flyweight pattern, the "Bold" `TextStyle` instance is only created once and shared among multiple `TextRange` instances, thereby saving memory. 68 | -------------------------------------------------------------------------------- /structural/flyweight/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | "sync" 6 | ) 7 | 8 | // TextStyle is a flyweight that represents a specific text style. 9 | type TextStyle struct { 10 | name string 11 | } 12 | 13 | // Format applies the text style to a text. 14 | func (t *TextStyle) Format(text string) string { 15 | return fmt.Sprintf("[%s %s]", t.name, text) 16 | } 17 | 18 | // TextStyleFactory creates and manages TextStyle instances. 19 | type TextStyleFactory struct { 20 | styles map[string]*TextStyle 21 | mu sync.Mutex 22 | } 23 | 24 | // GetTextStyle returns a TextStyle instance. It reuses an existing instance if available. 25 | func (f *TextStyleFactory) GetTextStyle(name string) *TextStyle { 26 | f.mu.Lock() 27 | defer f.mu.Unlock() 28 | 29 | if style, ok := f.styles[name]; ok { 30 | return style 31 | } 32 | 33 | style := &TextStyle{name: name} 34 | f.styles[name] = style 35 | return style 36 | } 37 | 38 | // TextRange represents a range of text within a document. 39 | type TextRange struct { 40 | Start, End int 41 | Text string 42 | Style *TextStyle 43 | } 44 | 45 | // NewTextRange creates a new text range. 46 | func NewTextRange(start, end int, text string, style *TextStyle) *TextRange { 47 | return &TextRange{ 48 | Start: start, 49 | End: end, 50 | Text: text, 51 | Style: style, 52 | } 53 | } 54 | 55 | // Format formats the text range with its text style. 56 | func (t *TextRange) Format() string { 57 | return t.Style.Format(t.Text) 58 | } 59 | 60 | func main() { 61 | factory := &TextStyleFactory{ 62 | styles: make(map[string]*TextStyle), 63 | } 64 | 65 | // Both text ranges share the same TextStyle instance. 66 | textRange1 := NewTextRange(0, 5, "Hello", factory.GetTextStyle("Bold")) 67 | textRange2 := NewTextRange(6, 11, "World", factory.GetTextStyle("Bold")) 68 | 69 | fmt.Println(textRange1.Format()) 70 | fmt.Println(textRange2.Format()) 71 | } 72 | -------------------------------------------------------------------------------- /structural/proxy/README.md: -------------------------------------------------------------------------------- 1 | # Proxy 2 | 3 | The proxy design pattern provides a surrogate or placeholder for another object to control access to it. It involves a class, called the proxy, which represents the functionality of another class. The proxy pattern is useful for tasks like lazy instantiation (creating an object only when it's actually needed), permission control, and more sophisticated memory management. 4 | 5 | Here's a simple breakdown of how the proxy pattern works: 6 | 7 | - The Subject defines a common interface for the RealObject and the Proxy so that the Proxy can be used anywhere the RealObject is expected. 8 | - The RealObject defines the real object that the proxy represents. 9 | - The Proxy maintains a reference that lets the proxy access the real object. It handles requests and forwards these requests to the real object. 10 | 11 | ## Example 12 | 13 | A practical example could be a system that interacts with an external service API. Without a proxy, every part of your code that needed to communicate with the API would have to know how to do so. With a proxy, you encapsulate the communication logic in one place, making the code cleaner and easier to maintain. 14 | 15 | Let's say you have a service that retrieves user information from a third-party API. You may want to implement a caching mechanism to avoid unnecessary network requests if the same data is requested multiple times. You can implement this with the proxy pattern. 16 | 17 | ```go 18 | type User struct { 19 | ID string 20 | Name string 21 | } 22 | 23 | type UserService interface { 24 | GetUser(ID string) (*User, error) 25 | } 26 | 27 | type RealUserService struct{} 28 | 29 | func (s *RealUserService) GetUser(ID string) (*User, error) { 30 | // Simulate a real API request 31 | fmt.Println("Fetching user from API...") 32 | return &User{ID: ID, Name: "John Doe"}, nil 33 | } 34 | 35 | type CachedUserService struct { 36 | realService UserService 37 | cache map[string]*User 38 | mux sync.Mutex 39 | } 40 | 41 | func (s *CachedUserService) GetUser(ID string) (*User, error) { 42 | s.mux.Lock() 43 | defer s.mux.Unlock() 44 | if user, ok := s.cache[ID]; ok { 45 | fmt.Println("Returning user from cache...") 46 | return user, nil 47 | } 48 | user, err := s.realService.GetUser(ID) 49 | if err != nil { 50 | return nil, err 51 | } 52 | s.cache[ID] = user 53 | return user, nil 54 | } 55 | 56 | func NewCachedUserService(service UserService) UserService { 57 | return &CachedUserService{ 58 | realService: service, 59 | cache: make(map[string]*User), 60 | } 61 | } 62 | ``` 63 | 64 | In this example, `UserService` is the interface for the user service, `RealUserService` fetches user data from the API, and `CachedUserService` is the proxy that adds caching. If the requested user data is in the cache, `CachedUserService` returns it without calling the real service. Otherwise, it fetches the data from `RealUserService`, stores it in the cache, and then returns it. 65 | -------------------------------------------------------------------------------- /structural/proxy/main.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "fmt" 5 | "sync" 6 | ) 7 | 8 | type User struct { 9 | ID string 10 | Name string 11 | } 12 | 13 | type UserService interface { 14 | GetUser(ID string) (*User, error) 15 | } 16 | 17 | type RealUserService struct{} 18 | 19 | func (s *RealUserService) GetUser(ID string) (*User, error) { 20 | // Simulate a real API request 21 | fmt.Println("Fetching user from API...") 22 | return &User{ID: ID, Name: "John Doe"}, nil 23 | } 24 | 25 | type CachedUserService struct { 26 | realService UserService 27 | cache map[string]*User 28 | mux sync.Mutex 29 | } 30 | 31 | func (s *CachedUserService) GetUser(ID string) (*User, error) { 32 | s.mux.Lock() 33 | defer s.mux.Unlock() 34 | if user, ok := s.cache[ID]; ok { 35 | fmt.Println("Returning user from cache...") 36 | return user, nil 37 | } 38 | user, err := s.realService.GetUser(ID) 39 | if err != nil { 40 | return nil, err 41 | } 42 | s.cache[ID] = user 43 | return user, nil 44 | } 45 | 46 | func NewCachedUserService(service UserService) UserService { 47 | return &CachedUserService{ 48 | realService: service, 49 | cache: make(map[string]*User), 50 | } 51 | } 52 | 53 | func main() { 54 | service := NewCachedUserService(&RealUserService{}) 55 | 56 | // Fetches from API 57 | service.GetUser("123") 58 | 59 | // Returns from cache 60 | service.GetUser("123") 61 | } 62 | --------------------------------------------------------------------------------