├── lazy_format.sublime-project ├── .travis.yml ├── .gitignore ├── Cargo.toml ├── README.md ├── CHANGELOG.md ├── tests └── tests.rs ├── LICENSE └── src └── lib.rs /lazy_format.sublime-project: -------------------------------------------------------------------------------- 1 | { 2 | "folders": 3 | [ 4 | { 5 | "path": "." 6 | } 7 | ] 8 | } 9 | -------------------------------------------------------------------------------- /.travis.yml: -------------------------------------------------------------------------------- 1 | language: rust 2 | 3 | rust: 4 | - stable 5 | - beta 6 | - nightly 7 | 8 | before_script: 9 | - rustup component add clippy 10 | 11 | script: 12 | - cargo clippy --verbose --all-features 13 | - cargo test --verbose --all-features 14 | 15 | matrix: 16 | allow_failures: 17 | - rust: nightly 18 | fast_finish: true 19 | -------------------------------------------------------------------------------- /.gitignore: -------------------------------------------------------------------------------- 1 | # Generated by Cargo 2 | # will have compiled files and executables 3 | /target/ 4 | 5 | # Remove Cargo.lock from gitignore if creating an executable, leave it for libraries 6 | # More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html 7 | Cargo.lock 8 | 9 | # These are backup files generated by rustfmt 10 | **/*.rs.bk 11 | -------------------------------------------------------------------------------- /Cargo.toml: -------------------------------------------------------------------------------- 1 | [package] 2 | name = "lazy_format" 3 | version = "2.0.3" 4 | authors = ["Nathan West "] 5 | edition = "2021" 6 | readme = "README.md" 7 | license = "MPL-2.0" 8 | description = "A utility crate for lazily formatting values for later" 9 | repository = "https://github.com/Lucretiel/lazy_format" 10 | categories = ["no-std", "rust-patterns", "value-formatting"] 11 | 12 | [badges] 13 | travis-ci = { repository = "Lucretiel/lazy_format" } 14 | maintenance = { status = "actively-developed" } 15 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | [![Travis (.com)](https://img.shields.io/travis/com/Lucretiel/lazy_format/master.svg)](https://travis-ci.com/Lucretiel/lazy_format/) 2 | [![Crates.io](https://img.shields.io/crates/v/lazy_format.svg?logo=rust&logoColor=white)](https://crates.io/crates/lazy_format) 3 | [![docs.rs](https://docs.rs/lazy_format/badge.svg)](https://docs.rs/lazy_format) 4 | [![license](https://img.shields.io/github/license/Lucretiel/lazy_format.svg)](https://crates.io/crates/lazy_format/) 5 | 6 | # lazy_format 7 | 8 | A `[no_std]` library for lazily formatting things. Because allocating temporary strings just to write them to a buffered stream is bad for your health. 9 | 10 | ```rust 11 | use std::io; 12 | 13 | use lazy_format::lazy_format; 14 | use joinery::JoinableIterator; 15 | 16 | fn main() { 17 | let result = (0..10) 18 | .map(|value| lazy_format!("\t'{}'", value)) 19 | .join_with("\n") 20 | .to_string(); 21 | 22 | assert_eq!(result, 23 | " '0' 24 | '1' 25 | '2' 26 | '3' 27 | '4' 28 | '5' 29 | '6' 30 | '7' 31 | '8' 32 | '9'") 33 | } 34 | ``` 35 | 36 | The above example is the key motivating example: when building up some kind of object you wish to write or format, there's no reason to allocate intermediary strings (which is what `format!` does). Instead, `lazy_format!` captures its arguments and returns an opaque struct with a `Display` implementation, so that the actual formatting can happen directly into its final destination buffer (such as a file or string). 37 | -------------------------------------------------------------------------------- /CHANGELOG.md: -------------------------------------------------------------------------------- 1 | # Changelog 2 | 3 | The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), 4 | and this project adheres to [Semantic Versioning 2.0.0](https://semver.org/spec/v2.0.0.html). 5 | 6 | ## 2.0.3 7 | 8 | ### Interal 9 | 10 | - Inline the compile-time check in `write`, to remove an unwanted export. 11 | 12 | ### Fixed 13 | 14 | - Fixed a bug where `{STYLE}` didn't format correctly. 15 | 16 | ## 2.0.2 17 | 18 | ### Internal 19 | 20 | - Redesign internal `write!` macro to ensure that format method short circuiting is _always_ evaluated at compile time, rather than relying on an optimization of an iterator call. 21 | 22 | ## 2.0.1 23 | 24 | ### Internal 25 | 26 | - Improved detecting of empty format strings 27 | 28 | ## 2.0.0 29 | 30 | What started as a simple collection of cleanup changes eventually spiraled out to the complete implementation of everything I've been looking to do for `lazy_format` 2.0. In particular, the improvements to `if` necessitated minor but technically backwards incompatible macro changes, which presented the opportunity to make the other backwards incompatible changes, like removing deprecated functionality and simplifying macro definitions. In general, if you're only using `lazy_format` and you aren't using `horrorshow`, you shouldn't experience any breakages in the upgrade. 31 | 32 | ### Added 33 | 34 | - `lazy_format` now supports implicit named parameters. Because we use `format_args!` internally, this support came automatically 35 | - `lazy_format`'s `if`, `match`, and `for` syntaxes now allow for unparenthesized format literals, in cases where there's no arguments. 36 | 37 | ### Changed 38 | 39 | - `lazy_format`'s `if` conditional version now allows omitting the `else` branch, in which case it will simply write nothing if none of the other `if` / `else if` branches match. 40 | - `lazy_format`'s `else` branch now requires the `=>` syntax, for consistency (previously it was optional). 41 | - Upgrade to Edition 2021. This means we can use the new `pat` pattern, which correctly handles nested `|` in patterns. This allows for much simpler macro definitions in a way that's fully backwards compatible (aside from the increased MSRV). 42 | 43 | ### Removed 44 | 45 | - **Breaking** Removed `semi_lazy_format`; the complexity of its implementation wasn't worth the added functionality. Instead, callers should manually evaluate any parameters they want to be eagerly evaluated before calling `lazy_format` and then pass them manually. 46 | - **Breaking** Removed `horrorshow` feature, due to potential buggy interactions with transitive dependencies. Prefer instead to create a `display` adapter which connects `Display` to `horrorshow`. 47 | - **Breaking** `semi_lazy_format!` no longer supports the deprecated `fmt => body` syntax; it now must use the `|fmt| body` syntax. 48 | 49 | ### Fixed 50 | 51 | - Fixed potential issue with ambiguous method call in the `for` loop version of `lazy_format` 52 | 53 | ## 1.10.0 54 | 55 | ### Added 56 | 57 | - `make_lazy_format!` now has a closure-like syntax, using `|f| { ... }` instead of `f => { ... }`. The older syntax is retained for backwards compatibility. 58 | 59 | ### Fixed 60 | 61 | - Fix an issue where formatting without arguments (e.g, `lazy_format!("{}")`) would succeed incorrectly ([#5](https://github.com/Lucretiel/lazy_format/issues/5)). 62 | - Thanks [@ten0](https://github.com/Ten0) for the report. 63 | 64 | ## 1.9.0 65 | 66 | - Changelog started 67 | -------------------------------------------------------------------------------- /tests/tests.rs: -------------------------------------------------------------------------------- 1 | /* 2 | * This Source Code Form is subject to the terms of the Mozilla Public 3 | * License, v. 2.0. If a copy of the MPL was not distributed with this 4 | * file, You can obtain one at https://mozilla.org/MPL/2.0/. 5 | */ 6 | 7 | // Copyright 2019-2022 Nathan West 8 | 9 | #![cfg(test)] 10 | 11 | use std::cell::Cell; 12 | 13 | // We put all the tests in a separate test crate, to ensure that macro imports 14 | // work correctly, and also to give us access to std 15 | 16 | #[derive(Debug, Clone, Default, Eq, PartialEq)] 17 | struct ValueEmitter { 18 | count: Cell, 19 | } 20 | 21 | impl ValueEmitter { 22 | fn new() -> Self { 23 | ValueEmitter { 24 | count: Cell::new(0), 25 | } 26 | } 27 | 28 | fn next(&self) -> String { 29 | self.count.set(self.count.get() + 1); 30 | format!("{}", self.count.get()) 31 | } 32 | 33 | fn count(&self) -> usize { 34 | self.count.get() 35 | } 36 | } 37 | 38 | mod lazy_format { 39 | use std::fmt::Display; 40 | use std::fmt::Write; 41 | 42 | use crate::ValueEmitter; 43 | use lazy_format::lazy_format; 44 | 45 | #[test] 46 | fn basic_format() { 47 | let mut dest = String::new(); 48 | write!( 49 | &mut dest, 50 | "{}", 51 | lazy_format!("{}, {value}", 123, value = "Hello, World") 52 | ) 53 | .unwrap(); 54 | assert_eq!(dest, "123, Hello, World"); 55 | } 56 | 57 | #[test] 58 | fn no_args_format() { 59 | let result = lazy_format!("Hello, World!").to_string(); 60 | assert_eq!(result, "Hello, World!"); 61 | } 62 | 63 | #[test] 64 | fn no_args_with_curlies() { 65 | let result = lazy_format!("{{ braces }}").to_string(); 66 | assert_eq!(result, "{ braces }") 67 | } 68 | 69 | #[test] 70 | fn ensure_lazy() { 71 | let emitter = &ValueEmitter::new(); 72 | 73 | let lazily_formatted = lazy_format!("{}, {} ({})", "Hello", "World", emitter.next()); 74 | let lazy2 = lazy_format!("{} {} {}", emitter.next(), emitter.next(), emitter.next()); 75 | 76 | // At this point, the cell should not have been incremented at all 77 | assert_eq!(emitter.count(), 0); 78 | 79 | // 80 | let mut dest = String::new(); 81 | write!(&mut dest, "{}\n{}", lazily_formatted, lazy2).unwrap(); 82 | assert_eq!(dest, "Hello, World (1)\n2 3 4"); 83 | assert_eq!(emitter.count(), 4); 84 | 85 | // Because the formatting is lazy, emitter.next() will continue to be called 86 | // every time the lazy_format values are formatted 87 | dest.clear(); 88 | write!(&mut dest, "{}\n{}", lazily_formatted, lazy2).unwrap(); 89 | assert_eq!(dest, "Hello, World (5)\n6 7 8"); 90 | assert_eq!(emitter.count(), 8); 91 | } 92 | 93 | #[test] 94 | fn test_recursive() { 95 | let emitter = &ValueEmitter::new(); 96 | 97 | let lazy1 = lazy_format!("{}, {}", emitter.next(), emitter.next()); 98 | let lazy2 = lazy_format!("({lazy}), ({lazy})", lazy = lazy1); 99 | let lazy3 = lazy_format!("({lazy}), ({lazy})", lazy = lazy2); 100 | 101 | assert_eq!(emitter.count(), 0); 102 | 103 | assert_eq!(lazy3.to_string(), "((1, 2), (3, 4)), ((5, 6), (7, 8))"); 104 | assert_eq!(emitter.count(), 8); 105 | 106 | assert_eq!( 107 | lazy3.to_string(), 108 | "((9, 10), (11, 12)), ((13, 14), (15, 16))" 109 | ); 110 | assert_eq!(emitter.count(), 16); 111 | } 112 | 113 | #[test] 114 | fn test_return_value() { 115 | let values = (0..5).map(|value| lazy_format!("'{}'... ", value)); 116 | 117 | let mut dest = String::new(); 118 | 119 | for value in values { 120 | write!(&mut dest, "{}", value).unwrap(); 121 | } 122 | 123 | assert_eq!(dest, "'0'... '1'... '2'... '3'... '4'... ") 124 | } 125 | 126 | #[test] 127 | fn test_result_value_with_lifetime() { 128 | // This function tests that the return value of lazy_format (and specifically 129 | // of make_lazy_format) fulfills the lifetime bound 130 | fn double_str(s: &str) -> impl Display + '_ { 131 | lazy_format!("{}, {}", s, s) 132 | } 133 | 134 | let content = "Hello".to_string(); 135 | let result = double_str(content.as_str()).to_string(); 136 | assert_eq!(result, "Hello, Hello"); 137 | } 138 | 139 | #[test] 140 | fn test_if_let() { 141 | fn describe_optional(value: Option) -> impl Display { 142 | lazy_format!( 143 | if let Some(3) | Some(4) = value => "Got a 3 or a 4" 144 | else if let Some(x) = value => "Got a value: {x}" 145 | else => "Got nothing" 146 | ) 147 | } 148 | 149 | assert_eq!(describe_optional(Some(3)).to_string(), "Got a 3 or a 4"); 150 | assert_eq!(describe_optional(Some(4)).to_string(), "Got a 3 or a 4"); 151 | assert_eq!(describe_optional(Some(10)).to_string(), "Got a value: 10"); 152 | assert_eq!(describe_optional(None).to_string(), "Got nothing") 153 | } 154 | 155 | #[test] 156 | fn test_if_else() { 157 | let value = 10; 158 | 159 | // This mostly exists to use "expand macro recursively" to check that 160 | // it correctly generates optimized write calls in these branches. A 161 | // future version of this test can actually test this by using a Write 162 | // adapter. 163 | let result = lazy_format!( 164 | if value == 10 => "ten" 165 | else if value > 10 => ("value: {}", value) 166 | else => "small" 167 | ); 168 | 169 | assert_eq!(result.to_string(), "ten"); 170 | } 171 | 172 | #[test] 173 | fn test_if_without_else() { 174 | let value = 0; 175 | 176 | let result = lazy_format!( 177 | if value == 10 => "10" 178 | else if value > 10 => "value: {value}" 179 | ); 180 | 181 | assert_eq!(result.to_string(), ""); 182 | } 183 | 184 | #[test] 185 | fn test_loop_underscore() { 186 | let result = lazy_format!("Ab" for _ in 0..5); 187 | assert_eq!(result.to_string(), "AbAbAbAbAb"); 188 | } 189 | 190 | #[test] 191 | fn test_contextual_loop() { 192 | let value = 10; 193 | let pairs = [('a', 'b'), ('c', 'd')]; 194 | let result = lazy_format!("{value} {left} {right}, " for &(left, right) in &pairs); 195 | assert_eq!(result.to_string(), "10 a b, 10 c d, ") 196 | } 197 | 198 | /// Test that the for loop version of lazy_format still works when the 199 | /// iterator type still has a try_for_each method, for some reason. 200 | #[test] 201 | fn test_bad_iterator() { 202 | #[derive(Copy, Clone)] 203 | struct Collection<'a> { 204 | slice: &'a [i32], 205 | } 206 | 207 | impl<'a> Iterator for Collection<'a> { 208 | type Item = &'a i32; 209 | 210 | fn next(&mut self) -> Option { 211 | self.slice.split_first().map(|(head, tail)| { 212 | self.slice = tail; 213 | head 214 | }) 215 | } 216 | } 217 | 218 | impl<'a> Collection<'a> { 219 | pub fn new(slice: &'a [i32]) -> Self { 220 | Self { slice } 221 | } 222 | 223 | #[allow(dead_code)] 224 | pub fn try_for_each(&mut self, _body: impl FnMut(&'a i32) -> T) -> T { 225 | panic!("This shouldn't be called") 226 | } 227 | } 228 | 229 | let collection = Collection::new(&[1, 2, 3, 4]); 230 | let output = lazy_format!("{item} " for item in collection); 231 | assert_eq!(output.to_string(), "1 2 3 4 "); 232 | } 233 | 234 | #[test] 235 | fn test_lazy_format_with_possible_name_collision() { 236 | const STYLE: i32 = 10; 237 | 238 | let s = lazy_format!("Value: {STYLE}").to_string(); 239 | 240 | assert_eq!(s, "Value: 10"); 241 | } 242 | } 243 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | Mozilla Public License Version 2.0 2 | ================================== 3 | 4 | 1. Definitions 5 | -------------- 6 | 7 | 1.1. "Contributor" 8 | means each individual or legal entity that creates, contributes to 9 | the creation of, or owns Covered Software. 10 | 11 | 1.2. "Contributor Version" 12 | means the combination of the Contributions of others (if any) used 13 | by a Contributor and that particular Contributor's Contribution. 14 | 15 | 1.3. "Contribution" 16 | means Covered Software of a particular Contributor. 17 | 18 | 1.4. "Covered Software" 19 | means Source Code Form to which the initial Contributor has attached 20 | the notice in Exhibit A, the Executable Form of such Source Code 21 | Form, and Modifications of such Source Code Form, in each case 22 | including portions thereof. 23 | 24 | 1.5. "Incompatible With Secondary Licenses" 25 | means 26 | 27 | (a) that the initial Contributor has attached the notice described 28 | in Exhibit B to the Covered Software; or 29 | 30 | (b) that the Covered Software was made available under the terms of 31 | version 1.1 or earlier of the License, but not also under the 32 | terms of a Secondary License. 33 | 34 | 1.6. "Executable Form" 35 | means any form of the work other than Source Code Form. 36 | 37 | 1.7. "Larger Work" 38 | means a work that combines Covered Software with other material, in 39 | a separate file or files, that is not Covered Software. 40 | 41 | 1.8. "License" 42 | means this document. 43 | 44 | 1.9. "Licensable" 45 | means having the right to grant, to the maximum extent possible, 46 | whether at the time of the initial grant or subsequently, any and 47 | all of the rights conveyed by this License. 48 | 49 | 1.10. "Modifications" 50 | means any of the following: 51 | 52 | (a) any file in Source Code Form that results from an addition to, 53 | deletion from, or modification of the contents of Covered 54 | Software; or 55 | 56 | (b) any new file in Source Code Form that contains any Covered 57 | Software. 58 | 59 | 1.11. "Patent Claims" of a Contributor 60 | means any patent claim(s), including without limitation, method, 61 | process, and apparatus claims, in any patent Licensable by such 62 | Contributor that would be infringed, but for the grant of the 63 | License, by the making, using, selling, offering for sale, having 64 | made, import, or transfer of either its Contributions or its 65 | Contributor Version. 66 | 67 | 1.12. "Secondary License" 68 | means either the GNU General Public License, Version 2.0, the GNU 69 | Lesser General Public License, Version 2.1, the GNU Affero General 70 | Public License, Version 3.0, or any later versions of those 71 | licenses. 72 | 73 | 1.13. "Source Code Form" 74 | means the form of the work preferred for making modifications. 75 | 76 | 1.14. "You" (or "Your") 77 | means an individual or a legal entity exercising rights under this 78 | License. For legal entities, "You" includes any entity that 79 | controls, is controlled by, or is under common control with You. For 80 | purposes of this definition, "control" means (a) the power, direct 81 | or indirect, to cause the direction or management of such entity, 82 | whether by contract or otherwise, or (b) ownership of more than 83 | fifty percent (50%) of the outstanding shares or beneficial 84 | ownership of such entity. 85 | 86 | 2. License Grants and Conditions 87 | -------------------------------- 88 | 89 | 2.1. Grants 90 | 91 | Each Contributor hereby grants You a world-wide, royalty-free, 92 | non-exclusive license: 93 | 94 | (a) under intellectual property rights (other than patent or trademark) 95 | Licensable by such Contributor to use, reproduce, make available, 96 | modify, display, perform, distribute, and otherwise exploit its 97 | Contributions, either on an unmodified basis, with Modifications, or 98 | as part of a Larger Work; and 99 | 100 | (b) under Patent Claims of such Contributor to make, use, sell, offer 101 | for sale, have made, import, and otherwise transfer either its 102 | Contributions or its Contributor Version. 103 | 104 | 2.2. Effective Date 105 | 106 | The licenses granted in Section 2.1 with respect to any Contribution 107 | become effective for each Contribution on the date the Contributor first 108 | distributes such Contribution. 109 | 110 | 2.3. Limitations on Grant Scope 111 | 112 | The licenses granted in this Section 2 are the only rights granted under 113 | this License. No additional rights or licenses will be implied from the 114 | distribution or licensing of Covered Software under this License. 115 | Notwithstanding Section 2.1(b) above, no patent license is granted by a 116 | Contributor: 117 | 118 | (a) for any code that a Contributor has removed from Covered Software; 119 | or 120 | 121 | (b) for infringements caused by: (i) Your and any other third party's 122 | modifications of Covered Software, or (ii) the combination of its 123 | Contributions with other software (except as part of its Contributor 124 | Version); or 125 | 126 | (c) under Patent Claims infringed by Covered Software in the absence of 127 | its Contributions. 128 | 129 | This License does not grant any rights in the trademarks, service marks, 130 | or logos of any Contributor (except as may be necessary to comply with 131 | the notice requirements in Section 3.4). 132 | 133 | 2.4. Subsequent Licenses 134 | 135 | No Contributor makes additional grants as a result of Your choice to 136 | distribute the Covered Software under a subsequent version of this 137 | License (see Section 10.2) or under the terms of a Secondary License (if 138 | permitted under the terms of Section 3.3). 139 | 140 | 2.5. Representation 141 | 142 | Each Contributor represents that the Contributor believes its 143 | Contributions are its original creation(s) or it has sufficient rights 144 | to grant the rights to its Contributions conveyed by this License. 145 | 146 | 2.6. Fair Use 147 | 148 | This License is not intended to limit any rights You have under 149 | applicable copyright doctrines of fair use, fair dealing, or other 150 | equivalents. 151 | 152 | 2.7. Conditions 153 | 154 | Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted 155 | in Section 2.1. 156 | 157 | 3. Responsibilities 158 | ------------------- 159 | 160 | 3.1. Distribution of Source Form 161 | 162 | All distribution of Covered Software in Source Code Form, including any 163 | Modifications that You create or to which You contribute, must be under 164 | the terms of this License. You must inform recipients that the Source 165 | Code Form of the Covered Software is governed by the terms of this 166 | License, and how they can obtain a copy of this License. You may not 167 | attempt to alter or restrict the recipients' rights in the Source Code 168 | Form. 169 | 170 | 3.2. Distribution of Executable Form 171 | 172 | If You distribute Covered Software in Executable Form then: 173 | 174 | (a) such Covered Software must also be made available in Source Code 175 | Form, as described in Section 3.1, and You must inform recipients of 176 | the Executable Form how they can obtain a copy of such Source Code 177 | Form by reasonable means in a timely manner, at a charge no more 178 | than the cost of distribution to the recipient; and 179 | 180 | (b) You may distribute such Executable Form under the terms of this 181 | License, or sublicense it under different terms, provided that the 182 | license for the Executable Form does not attempt to limit or alter 183 | the recipients' rights in the Source Code Form under this License. 184 | 185 | 3.3. Distribution of a Larger Work 186 | 187 | You may create and distribute a Larger Work under terms of Your choice, 188 | provided that You also comply with the requirements of this License for 189 | the Covered Software. If the Larger Work is a combination of Covered 190 | Software with a work governed by one or more Secondary Licenses, and the 191 | Covered Software is not Incompatible With Secondary Licenses, this 192 | License permits You to additionally distribute such Covered Software 193 | under the terms of such Secondary License(s), so that the recipient of 194 | the Larger Work may, at their option, further distribute the Covered 195 | Software under the terms of either this License or such Secondary 196 | License(s). 197 | 198 | 3.4. Notices 199 | 200 | You may not remove or alter the substance of any license notices 201 | (including copyright notices, patent notices, disclaimers of warranty, 202 | or limitations of liability) contained within the Source Code Form of 203 | the Covered Software, except that You may alter any license notices to 204 | the extent required to remedy known factual inaccuracies. 205 | 206 | 3.5. Application of Additional Terms 207 | 208 | You may choose to offer, and to charge a fee for, warranty, support, 209 | indemnity or liability obligations to one or more recipients of Covered 210 | Software. However, You may do so only on Your own behalf, and not on 211 | behalf of any Contributor. You must make it absolutely clear that any 212 | such warranty, support, indemnity, or liability obligation is offered by 213 | You alone, and You hereby agree to indemnify every Contributor for any 214 | liability incurred by such Contributor as a result of warranty, support, 215 | indemnity or liability terms You offer. You may include additional 216 | disclaimers of warranty and limitations of liability specific to any 217 | jurisdiction. 218 | 219 | 4. Inability to Comply Due to Statute or Regulation 220 | --------------------------------------------------- 221 | 222 | If it is impossible for You to comply with any of the terms of this 223 | License with respect to some or all of the Covered Software due to 224 | statute, judicial order, or regulation then You must: (a) comply with 225 | the terms of this License to the maximum extent possible; and (b) 226 | describe the limitations and the code they affect. Such description must 227 | be placed in a text file included with all distributions of the Covered 228 | Software under this License. Except to the extent prohibited by statute 229 | or regulation, such description must be sufficiently detailed for a 230 | recipient of ordinary skill to be able to understand it. 231 | 232 | 5. Termination 233 | -------------- 234 | 235 | 5.1. The rights granted under this License will terminate automatically 236 | if You fail to comply with any of its terms. However, if You become 237 | compliant, then the rights granted under this License from a particular 238 | Contributor are reinstated (a) provisionally, unless and until such 239 | Contributor explicitly and finally terminates Your grants, and (b) on an 240 | ongoing basis, if such Contributor fails to notify You of the 241 | non-compliance by some reasonable means prior to 60 days after You have 242 | come back into compliance. Moreover, Your grants from a particular 243 | Contributor are reinstated on an ongoing basis if such Contributor 244 | notifies You of the non-compliance by some reasonable means, this is the 245 | first time You have received notice of non-compliance with this License 246 | from such Contributor, and You become compliant prior to 30 days after 247 | Your receipt of the notice. 248 | 249 | 5.2. If You initiate litigation against any entity by asserting a patent 250 | infringement claim (excluding declaratory judgment actions, 251 | counter-claims, and cross-claims) alleging that a Contributor Version 252 | directly or indirectly infringes any patent, then the rights granted to 253 | You by any and all Contributors for the Covered Software under Section 254 | 2.1 of this License shall terminate. 255 | 256 | 5.3. In the event of termination under Sections 5.1 or 5.2 above, all 257 | end user license agreements (excluding distributors and resellers) which 258 | have been validly granted by You or Your distributors under this License 259 | prior to termination shall survive termination. 260 | 261 | ************************************************************************ 262 | * * 263 | * 6. Disclaimer of Warranty * 264 | * ------------------------- * 265 | * * 266 | * Covered Software is provided under this License on an "as is" * 267 | * basis, without warranty of any kind, either expressed, implied, or * 268 | * statutory, including, without limitation, warranties that the * 269 | * Covered Software is free of defects, merchantable, fit for a * 270 | * particular purpose or non-infringing. The entire risk as to the * 271 | * quality and performance of the Covered Software is with You. * 272 | * Should any Covered Software prove defective in any respect, You * 273 | * (not any Contributor) assume the cost of any necessary servicing, * 274 | * repair, or correction. This disclaimer of warranty constitutes an * 275 | * essential part of this License. No use of any Covered Software is * 276 | * authorized under this License except under this disclaimer. * 277 | * * 278 | ************************************************************************ 279 | 280 | ************************************************************************ 281 | * * 282 | * 7. Limitation of Liability * 283 | * -------------------------- * 284 | * * 285 | * Under no circumstances and under no legal theory, whether tort * 286 | * (including negligence), contract, or otherwise, shall any * 287 | * Contributor, or anyone who distributes Covered Software as * 288 | * permitted above, be liable to You for any direct, indirect, * 289 | * special, incidental, or consequential damages of any character * 290 | * including, without limitation, damages for lost profits, loss of * 291 | * goodwill, work stoppage, computer failure or malfunction, or any * 292 | * and all other commercial damages or losses, even if such party * 293 | * shall have been informed of the possibility of such damages. This * 294 | * limitation of liability shall not apply to liability for death or * 295 | * personal injury resulting from such party's negligence to the * 296 | * extent applicable law prohibits such limitation. Some * 297 | * jurisdictions do not allow the exclusion or limitation of * 298 | * incidental or consequential damages, so this exclusion and * 299 | * limitation may not apply to You. * 300 | * * 301 | ************************************************************************ 302 | 303 | 8. Litigation 304 | ------------- 305 | 306 | Any litigation relating to this License may be brought only in the 307 | courts of a jurisdiction where the defendant maintains its principal 308 | place of business and such litigation shall be governed by laws of that 309 | jurisdiction, without reference to its conflict-of-law provisions. 310 | Nothing in this Section shall prevent a party's ability to bring 311 | cross-claims or counter-claims. 312 | 313 | 9. Miscellaneous 314 | ---------------- 315 | 316 | This License represents the complete agreement concerning the subject 317 | matter hereof. If any provision of this License is held to be 318 | unenforceable, such provision shall be reformed only to the extent 319 | necessary to make it enforceable. Any law or regulation which provides 320 | that the language of a contract shall be construed against the drafter 321 | shall not be used to construe this License against a Contributor. 322 | 323 | 10. Versions of the License 324 | --------------------------- 325 | 326 | 10.1. New Versions 327 | 328 | Mozilla Foundation is the license steward. Except as provided in Section 329 | 10.3, no one other than the license steward has the right to modify or 330 | publish new versions of this License. Each version will be given a 331 | distinguishing version number. 332 | 333 | 10.2. Effect of New Versions 334 | 335 | You may distribute the Covered Software under the terms of the version 336 | of the License under which You originally received the Covered Software, 337 | or under the terms of any subsequent version published by the license 338 | steward. 339 | 340 | 10.3. Modified Versions 341 | 342 | If you create software not governed by this License, and you want to 343 | create a new license for such software, you may create and use a 344 | modified version of this License if you rename the license and remove 345 | any references to the name of the license steward (except to note that 346 | such modified license differs from this License). 347 | 348 | 10.4. Distributing Source Code Form that is Incompatible With Secondary 349 | Licenses 350 | 351 | If You choose to distribute Source Code Form that is Incompatible With 352 | Secondary Licenses under the terms of this version of the License, the 353 | notice described in Exhibit B of this License must be attached. 354 | 355 | Exhibit A - Source Code Form License Notice 356 | ------------------------------------------- 357 | 358 | This Source Code Form is subject to the terms of the Mozilla Public 359 | License, v. 2.0. If a copy of the MPL was not distributed with this 360 | file, You can obtain one at http://mozilla.org/MPL/2.0/. 361 | 362 | If it is not possible or desirable to put the notice in a particular 363 | file, then You may include the notice in a location (such as a LICENSE 364 | file in a relevant directory) where a recipient would be likely to look 365 | for such a notice. 366 | 367 | You may add additional accurate notices of copyright ownership. 368 | 369 | Exhibit B - "Incompatible With Secondary Licenses" Notice 370 | --------------------------------------------------------- 371 | 372 | This Source Code Form is "Incompatible With Secondary Licenses", as 373 | defined by the Mozilla Public License, v. 2.0. 374 | -------------------------------------------------------------------------------- /src/lib.rs: -------------------------------------------------------------------------------- 1 | /* 2 | * This Source Code Form is subject to the terms of the Mozilla Public 3 | * License, v. 2.0. If a copy of the MPL was not distributed with this 4 | * file, You can obtain one at https://mozilla.org/MPL/2.0/. 5 | */ 6 | 7 | // Copyright 2019-2022 Nathan West 8 | 9 | #![no_std] 10 | 11 | /*! 12 | [`lazy_format!`] is a [`format!`]-style macro which lazily formats its 13 | arguments. That is, rather than immediatly formatting them into a [`String`] 14 | (which is what [`format!`] does), it captures its arguments and returns an 15 | opaque struct with a [`Display`] implementation, so that the actual formatting 16 | can happen directly into its final destination buffer (such as a file or 17 | string). 18 | 19 | ``` 20 | use std::fmt::Display; 21 | 22 | use lazy_format::prelude::*; 23 | 24 | // NOTE: This is profoundly insecure and you should never actually 25 | // render HTML without escape guards, code injection prevention, etc. 26 | fn html_tag<'a>(tag: &'a str, content: impl Display + 'a) -> impl Display + 'a { 27 | lazy_format!("<{tag}>{content}") 28 | } 29 | 30 | let result = html_tag("div", html_tag("p", "Hello, World!")).to_string(); 31 | assert_eq!(result, "

Hello, World!

"); 32 | ``` 33 | 34 | [`format!`]: https://doc.rust-lang.org/std/macro.format.html 35 | [`Display`]: https://doc.rust-lang.org/std/fmt/trait.Display.html 36 | [`String`]: https://doc.rust-lang.org/std/string/struct.String.html 37 | */ 38 | 39 | /** 40 | Smarter write macro. Encodes some common patterns, such as writing an empty 41 | string being a no-op. Used in the more complex lazy-format operations, like 42 | conditionals, where writing only strings or empty strings, is common. 43 | */ 44 | #[macro_export] 45 | #[doc(hidden)] 46 | macro_rules! write { 47 | ($dest:expr, "" $(,)? ) => { ::core::fmt::Result::Ok(()) }; 48 | 49 | ($dest:expr, $pattern:literal $(,)? ) => {{ 50 | enum Style { 51 | Empty, 52 | Plain, 53 | Format, 54 | } 55 | 56 | match { 57 | // We want this to be const so that we can guarantee it's computed 58 | // at compile time. Need to put the `STYLE` global in a nested 59 | // scope because otherwise it leaks out 60 | const STYLE: Style = match $pattern.as_bytes().split_first() { 61 | ::core::option::Option::None => Style::Empty, 62 | ::core::option::Option::Some((&(b'}' | b'{'), _)) => Style::Format, 63 | ::core::option::Option::Some((_, mut s)) => loop { 64 | s = match s.split_first() { 65 | None => break Style::Plain, 66 | Some((&(b'}' | b'{'), _)) => break Style::Format, 67 | Some((_, s)) => s, 68 | }; 69 | } 70 | }; 71 | 72 | STYLE 73 | } { 74 | Style::Empty => ::core::fmt::Result::Ok(()), 75 | Style::Plain => ::core::fmt::Write::write_str($dest, $pattern), 76 | Style::Format => ::core::fmt::Write::write_fmt($dest, ::core::format_args!($pattern)), 77 | } 78 | }}; 79 | 80 | ($dest:expr, $pattern:literal, $($args:tt)+ ) => { 81 | ::core::fmt::Write::write_fmt($dest, ::core::format_args!($pattern, $($args)+)) 82 | }; 83 | } 84 | 85 | /** 86 | Helper macro for common formatting shortcuts. In a few places in lazy_format, 87 | it's permitted to write either `lazy_format!(if cond => "foo")` or 88 | `lazy_format!(if cond => ("value: {}", value))`. This macro takes care of 89 | handling both cases. 90 | */ 91 | #[macro_export] 92 | #[doc(hidden)] 93 | macro_rules! write_tt { 94 | ($dest:expr, $pattern:literal) => { $crate::write!($dest, $pattern) }; 95 | ($dest:expr, ($pattern:literal $($args:tt)*)) => { $crate::write!($dest, $pattern $($args)*) }; 96 | } 97 | 98 | /// Test that an empty format string succeeds unconditionally. 99 | #[test] 100 | fn test_write_tt_empty_pattern() { 101 | use core::fmt; 102 | 103 | struct BadDest; 104 | 105 | impl fmt::Write for BadDest { 106 | fn write_str(&mut self, _s: &str) -> fmt::Result { 107 | Err(fmt::Error) 108 | } 109 | } 110 | 111 | let x = 10; 112 | 113 | write_tt!(&mut BadDest, "").unwrap(); 114 | write_tt!(&mut BadDest, ("")).unwrap(); 115 | write_tt!(&mut BadDest, ("",)).unwrap(); 116 | 117 | write_tt!(&mut BadDest, "Plain String").unwrap_err(); 118 | write_tt!(&mut BadDest, "Formatted String: {x}").unwrap_err(); 119 | } 120 | 121 | #[test] 122 | fn test_write_string_pattern() { 123 | use core::fmt; 124 | 125 | struct WeirdDest; 126 | 127 | impl fmt::Write for WeirdDest { 128 | fn write_str(&mut self, _s: &str) -> fmt::Result { 129 | Ok(()) 130 | } 131 | 132 | fn write_fmt(&mut self, _args: fmt::Arguments<'_>) -> fmt::Result { 133 | Err(fmt::Error) 134 | } 135 | } 136 | 137 | let x = 10; 138 | 139 | write_tt!(&mut WeirdDest, "Plain String").unwrap(); 140 | write_tt!(&mut WeirdDest, "Formatted String: {x}").unwrap_err(); 141 | } 142 | 143 | /** 144 | Low level constructor for lazy format instances. Create a lazy formatter with a 145 | custom closure as its [`Display`] implementation, for complete control over 146 | formatting behavior at write time. 147 | 148 | [`make_lazy_format!`] is the low-level constructor for lazy format instances. It 149 | is completely customizable, insofar as it allows you to create a custom 150 | [`Display::fmt`] implementation at the call site. 151 | 152 | [`make_lazy_format!`] takes a closure as an argument, and creates a [`Display`] 153 | struct that captures the local environment in a closure and uses it as the 154 | formatting function. 155 | 156 | # Example: 157 | 158 | ``` 159 | use std::fmt::Display; 160 | use lazy_format::make_lazy_format; 161 | 162 | let data = vec![1, 2, 3, 4, 5]; 163 | 164 | let comma_separated = make_lazy_format!(|f| { 165 | let mut iter = data.iter(); 166 | match iter.next() { 167 | None => Ok(()), 168 | Some(first) => { 169 | write!(f, "{}", first)?; 170 | iter.try_for_each(|value| write!(f, ", {}", value)) 171 | } 172 | } 173 | }); 174 | 175 | let result = comma_separated.to_string(); 176 | 177 | assert_eq!(result, "1, 2, 3, 4, 5"); 178 | ``` 179 | 180 | [`Display`]: https://doc.rust-lang.org/std/fmt/trait.Display.html 181 | [`Display::fmt`]: https://doc.rust-lang.org/core/fmt/trait.Display.html#tymethod.fmt 182 | */ 183 | #[macro_export] 184 | macro_rules! make_lazy_format { 185 | (|$fmt:ident| $write:expr) => {{ 186 | #[derive(Clone, Copy)] 187 | struct LazyFormat ::core::fmt::Result>(F); 188 | 189 | // TODO: customize Debug impl for semi_lazy_format to include value 190 | impl ::core::fmt::Result> ::core::fmt::Debug 191 | for LazyFormat 192 | { 193 | #[inline] 194 | fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result { 195 | f.write_str(concat!( 196 | "make_lazy_format!(", 197 | stringify!(|$fmt| $write), 198 | ")" 199 | )) 200 | } 201 | } 202 | 203 | impl ::core::fmt::Result> ::core::fmt::Display 204 | for LazyFormat 205 | { 206 | #[inline] 207 | fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result { 208 | (self.0)(f) 209 | } 210 | } 211 | 212 | LazyFormat(move |$fmt: &mut ::core::fmt::Formatter| -> ::core::fmt::Result { $write }) 213 | }}; 214 | } 215 | 216 | /** 217 | Lazily format something. Essentially the same as [`format!`], except that 218 | instead of formatting its arguments to a string, it captures them in an opaque 219 | struct, which can be formatted later. This allows you to build up formatting 220 | operations without any intermediary allocations or extra formatting calls. Also 221 | supports lazy conditional and looping constructs. 222 | 223 | The return value of this macro is left deliberately unspecified and 224 | undocumented. The most important this about it is its [`Display`] 225 | implementation, which executes the deferred formatting operation. It also 226 | provides a [`Debug`] implementation, which simply prints the 227 | [`lazy_format!`]`(...)` call without evaluating any of its arguments, as well 228 | as [`Clone`] and [`Copy`] if those traits are available in the captured 229 | context. 230 | 231 | Note that this macro is completely lazy; it captures the expressions to 232 | be formatted in the struct and doesn't evaluate them until the struct is 233 | actually written to a [`String`] or [`File`] or or other writable destination. 234 | This means that the argument expression will be evaluated *every* time the 235 | instance is written, which may not be what you want; be sure to eagerly perform 236 | any 1-time calculations you want to before calling `lazy_format!`. 237 | 238 | # Basic example: 239 | 240 | ``` 241 | use std::fmt::Display; 242 | use lazy_format::lazy_format; 243 | 244 | fn get_hello() -> String { 245 | String::from("Hello") 246 | } 247 | 248 | fn get_world() -> String { 249 | String::from("World") 250 | } 251 | 252 | fn hello_world() -> impl Display { 253 | lazy_format!("{}, {w}!", get_hello(), w = get_world()) 254 | } 255 | 256 | let result = hello_world(); 257 | 258 | // get_hello and get_world aren't called until the object is 259 | // formatted into a String. 260 | let result_str = result.to_string(); 261 | assert_eq!(result_str, "Hello, World!"); 262 | ``` 263 | 264 | Just like with regular formatting, `lazy_format` can automatically, implicitly 265 | capture named parameters: 266 | 267 | ``` 268 | use std::mem::{size_of_val, size_of}; 269 | use lazy_format::lazy_format; 270 | 271 | let a = 10; 272 | let b = 20; 273 | 274 | let result = lazy_format!("{a} {b}"); 275 | assert_eq!(size_of_val(&result), size_of::() * 2); 276 | assert_eq!(result.to_string(), "10 20"); 277 | ``` 278 | 279 | # Demonstation of lazy capturing: 280 | 281 | ``` 282 | use std::fmt::Display; 283 | use std::mem::{size_of_val, size_of}; 284 | use lazy_format::lazy_format; 285 | 286 | 287 | fn get_formatted() -> impl Display { 288 | let a: isize = 10; 289 | let b: isize = 15; 290 | 291 | lazy_format!("10 + 15: {v}, again: {v}", v = (a + b)) 292 | } 293 | 294 | let result = get_formatted(); 295 | 296 | // The result captures 2 isize values (a and b) from get_formatted. 297 | assert_eq!(size_of_val(&result), size_of::() * 2); 298 | 299 | let result_str = result.to_string(); 300 | assert_eq!(result_str, "10 + 15: 25, again: 25"); 301 | ``` 302 | 303 | # Conditional formatting 304 | 305 | `lazy_format!` supports conditional formatting with `match`- or `if`- 306 | style syntax. When doing a conditional format, add the formatting pattern 307 | and arguments directly into the `match` arms or `if` blocks, rather than 308 | code; this allows conditional formatting to still be captured in a single 309 | static type. 310 | 311 | ## `match` conditional example: 312 | 313 | ``` 314 | use std::fmt::Display; 315 | use lazy_format::lazy_format; 316 | 317 | fn get_number(num: usize) -> impl Display { 318 | // Note that the parenthesis in the match conditional are required, 319 | // due to limitations in Rust's macro parsing (can't follow an 320 | // expression with `{}`) 321 | lazy_format!(match (num) { 322 | 0 => "Zero", 323 | 1 => "One", 324 | 2 => "Two", 325 | 3 => "Three", 326 | 4 | 5 => "Four or five", 327 | value if value % 2 == 0 => ("A large even number: {}", value), 328 | value => "An unrecognized number: {value}", 329 | }) 330 | } 331 | 332 | assert_eq!(get_number(0).to_string(), "Zero"); 333 | assert_eq!(get_number(1).to_string(), "One"); 334 | assert_eq!(get_number(2).to_string(), "Two"); 335 | assert_eq!(get_number(3).to_string(), "Three"); 336 | assert_eq!(get_number(4).to_string(), "Four or five"); 337 | assert_eq!(get_number(5).to_string(), "Four or five"); 338 | assert_eq!(get_number(6).to_string(), "A large even number: 6"); 339 | assert_eq!(get_number(7).to_string(), "An unrecognized number: 7"); 340 | ``` 341 | 342 | ## `if` conditional example: 343 | 344 | ``` 345 | use std::fmt::Display; 346 | use lazy_format::lazy_format; 347 | 348 | fn describe_number(value: isize) -> impl Display { 349 | lazy_format!( 350 | if value < 0 => ("A negative number: {}", value) 351 | else if value % 3 == 0 => ("A number divisible by 3: {}", value) 352 | else if value % 2 == 1 => ("An odd number: {}", value) 353 | else => "Some other kind of number" 354 | ) 355 | } 356 | 357 | assert_eq!(describe_number(-2).to_string(), "A negative number: -2"); 358 | assert_eq!(describe_number(-1).to_string(), "A negative number: -1"); 359 | assert_eq!(describe_number(0).to_string(), "A number divisible by 3: 0"); 360 | assert_eq!(describe_number(1).to_string(), "An odd number: 1"); 361 | assert_eq!(describe_number(2).to_string(), "Some other kind of number"); 362 | assert_eq!(describe_number(3).to_string(), "A number divisible by 3: 3"); 363 | ``` 364 | 365 | `if` formatters are allowed to exclude the final `else` branch, in which 366 | case `lazy_format` will simply write an empty string: 367 | 368 | ``` 369 | use std::fmt::Display; 370 | use lazy_format::lazy_format; 371 | 372 | fn only_evens(value: i32) -> impl Display { 373 | lazy_format!(if value % 2 == 0 => ("An even number: {}", value)) 374 | } 375 | 376 | assert_eq!(only_evens(10).to_string(), "An even number: 10"); 377 | assert_eq!(only_evens(5).to_string(), ""); 378 | ``` 379 | 380 | ## `if let` conditional example: 381 | 382 | ``` 383 | use std::fmt::Display; 384 | use lazy_format::lazy_format; 385 | 386 | fn describe_optional_number(value: Option) -> impl Display { 387 | lazy_format!( 388 | if let Some(10) = value => "It's ten!" 389 | else if let Some(3) | Some(4) = value => "It's three or four!" 390 | else if let | Some(0) = value => "It's zero!" 391 | else if let Some(x) = value => ("It's some other value: {}", x) 392 | else => "It's not a number!" 393 | ) 394 | } 395 | 396 | assert_eq!(describe_optional_number(Some(10)).to_string(), "It's ten!"); 397 | assert_eq!(describe_optional_number(Some(3)).to_string(), "It's three or four!"); 398 | assert_eq!(describe_optional_number(Some(4)).to_string(), "It's three or four!"); 399 | assert_eq!(describe_optional_number(Some(0)).to_string(), "It's zero!"); 400 | assert_eq!(describe_optional_number(Some(5)).to_string(), "It's some other value: 5"); 401 | assert_eq!(describe_optional_number(None).to_string(), "It's not a number!"); 402 | ``` 403 | 404 | # Looping formatting 405 | 406 | `lazy_format!` supports formatting elements in a collection with a loop: 407 | 408 | ``` 409 | use std::fmt::Display; 410 | use lazy_format::lazy_format; 411 | 412 | let list = vec![1i32, 2, 3, 4]; 413 | let list_ref = &list; 414 | 415 | // Format each element in the iterable without additional arguments to `format_args` 416 | let simple_semicolons = lazy_format!("{v}; " for v in list_ref.iter().map(|x| x - 1)); 417 | assert_eq!(simple_semicolons.to_string(), "0; 1; 2; 3; "); 418 | 419 | // Perform a full format with additional arguments on each element in the iterable. 420 | let header = "Value"; 421 | let full_format = lazy_format!(("{}: {}; ", header, v) for v in list_ref); 422 | assert_eq!(full_format.to_string(), "Value: 1; Value: 2; Value: 3; Value: 4; "); 423 | ``` 424 | 425 | Note that these looping formatters are not suitable for doing something like 426 | a comma separated list, since they'll apply the formatting to all elements. 427 | For a lazy string joining library, which only inserts separators between 428 | elements in a list, check out [joinery](/joinery). 429 | 430 | [`format!`]: https://doc.rust-lang.org/std/macro.format.html 431 | [`Display`]: https://doc.rust-lang.org/std/fmt/trait.Display.html 432 | [`Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html 433 | [`String`]: https://doc.rust-lang.org/std/string/struct.String.html 434 | [`File`]: https://doc.rust-lang.org/std/fs/struct.File.html 435 | */ 436 | #[macro_export] 437 | macro_rules! lazy_format { 438 | // Basic lazy format: collect $args and format via `$pattern` when writing 439 | // to a destination 440 | ($pattern:literal $(, $($args:tt)*)?) => { 441 | $crate::make_lazy_format!(|f| $crate::write!(f, $pattern $(, $($args)*)?)) 442 | }; 443 | 444 | // Conditional lazy format: evaluate a match expression and format based on 445 | // the matching arm 446 | (match ($condition:expr) { 447 | $($( 448 | $match_pattern:pat 449 | $(if $guard:expr)? 450 | => $output:tt 451 | ),+ $(,)?)? 452 | }) => { 453 | $crate::make_lazy_format!(|f| match $condition { 454 | $($( 455 | $match_pattern 456 | $(if $guard)? 457 | => $crate::write_tt!(f, $output), 458 | )+)? 459 | }) 460 | }; 461 | 462 | // Conditional pattern lazy format: evaluate 463 | 464 | // Conditional lazy format: evaluate an if / else if / else expression and 465 | // format based on the successful branch 466 | ( 467 | if $(let $match:pat = )? $condition:expr => $output:tt 468 | $(else if $(let $elseif_match:pat = )? $elseif_condition:expr => $elseif_output:tt)* 469 | $(else => $else_output:tt)? 470 | ) => { 471 | $crate::make_lazy_format!(|f| 472 | if $(let $match = )? $condition { 473 | $crate::write_tt!(f, $output) 474 | } 475 | $(else if $(let $elseif_match = )? $elseif_condition { 476 | $crate::write_tt!(f, $elseif_output) 477 | })* 478 | $(else if true { 479 | $crate::write_tt!(f, $else_output) 480 | })? 481 | else { 482 | ::core::fmt::Result::Ok(()) 483 | } 484 | ) 485 | }; 486 | 487 | // Looping formatter: format each `$item` in `$collection` with the format 488 | // arguments 489 | ($output:tt for $item:pat in $collection:expr) => { 490 | $crate::make_lazy_format!(|f| { 491 | let mut iter = ::core::iter::IntoIterator::into_iter($collection); 492 | ::core::iter::Iterator::try_for_each(&mut iter, |$item| $crate::write_tt!(f, $output)) 493 | }) 494 | }; 495 | } 496 | 497 | pub mod prelude { 498 | pub use crate::{lazy_format, make_lazy_format}; 499 | } 500 | --------------------------------------------------------------------------------