├── .gitignore ├── example-readme-1.cpp ├── example-all-elements.cpp ├── README.md ├── html++.h └── LICENSE /.gitignore: -------------------------------------------------------------------------------- 1 | *~ 2 | *# 3 | example-readme-1 4 | example-all-elements 5 | -------------------------------------------------------------------------------- /example-readme-1.cpp: -------------------------------------------------------------------------------- 1 | #include 2 | #include "html++.h" 3 | 4 | int main() 5 | { 6 | html< 7 | head< 8 | title<"Help Me."> 9 | >, 10 | body< 11 | h1<"The horror!">, 12 | p<"Someone has probably done this before, but I can see why it didn't catch on.">, 13 | a<"href=https://github.com/csb6/html-plus-plus", "For science"> 14 | > 15 | > page; 16 | 17 | std::cout << page.content; 18 | 19 | return 0; 20 | } 21 | -------------------------------------------------------------------------------- /example-all-elements.cpp: -------------------------------------------------------------------------------- 1 | #include 2 | #include "html++.h" 3 | 4 | int main() 5 | { 6 | constexpr char panda_url[] = "src='https://upload.wikimedia.org/wikipedia/commons/f/fa/Panda_bear_at_memphis_zoo.JPG'"; 7 | 8 | html< 9 | head< 10 | title<"HTML++ = C++ Templates + HTML"> 11 | >, 12 | body< 13 | h1<"This was a mistake">, 14 | h2<"Here are some pictures:">, 15 | img, 16 | br, 17 | h2<"Here is some text">, 18 | div_< 19 | p<"Hello, World!">, 20 | p<"Yes, this document structure has been typechecked :)"> 21 | >, 22 | a<"href='https://en.cppreference.com/'", "This website is helpful"> 23 | > 24 | > page; 25 | 26 | std::cout << page.content; 27 | 28 | return 0; 29 | } 30 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # HTML++ 2 | 3 | Write HTML using C++ templates. The HTML document is represented as a single, 4 | deeply-nested type which is type-checked by the compiler using certain rules about how 5 | HTML elements are allowed to be nested (e.g. nothing can be a child of a `
` tag). 6 | 7 | If compilation succeeds, you will have a program that prints a properly-indented 8 | HTML document to the standard output when run. 9 | 10 | ## Example 11 | 12 | Say you want to write the following HTML page: 13 | 14 | ```html 15 | 16 | 17 | Help Me. 18 | 19 | 20 |

The horror!

21 |

22 | Someone has probably done this before, but I can see why it didn't catch on. 23 |

24 | For science 25 | 26 | 27 | ``` 28 | 29 | Here is a C++ program that can be used to generate that page: 30 | 31 | ```cpp 32 | #include 33 | #include "html++.h" 34 | 35 | int main() 36 | { 37 | html< 38 | head< 39 | title<"Help Me."> 40 | >, 41 | body< 42 | h1<"The horror!">, 43 | p<"Someone has probably done this before, but I can see why it didn't catch on.">, 44 | a<"href=https://github.com/csb6/html-plus-plus", "For science"> 45 | > 46 | > page; 47 | 48 | 49 | std::cout << page.content; 50 | 51 | return 0; 52 | } 53 | ``` 54 | 55 | ## Installation 56 | 57 | This library requires C++20. It works with GCC 9.2.0 with `-std=c++2a` enabled. 58 | It doesn't work with Apple Clang 11.0, but it might work on other compilers. If 59 | C++20 is fully implemented on a given compiler, it should be able to compile. 60 | 61 | Simply `#include html++.h`. It is the only file you need. 62 | 63 | ## Questions 64 | 65 | ### Why 66 | 67 | I was writing some HTML, and I realized that the structure and syntax of 68 | HTML tags was quite a bit like the structure/syntax of C++ templates. Both 69 | enable you to nest identifiers into a tree structure. 70 | 71 | Since variadic templates were added to C++, a template can hold any 72 | number of other types in a parameter pack, enabling parent nodes to hold any 73 | number of child nodes. This is necessary in order for HTML elements to be 74 | properly represented by C++ types. 75 | 76 | Since C++20, it is now possible to use string literals as non-type template 77 | parameters (e.g. `h1<"This is a title">`), making C++ templates capable of 78 | imitating the appearance of HTML tags even more closely. 79 | 80 | I thought I'd see how horrible it would be, and, as expected, it is pretty 81 | ridiculous. 82 | 83 | ### How 84 | 85 | The entire library is basically a fancy way of concatenating strings. 86 | Each tag is defined as its own template struct 87 | (e.g. `template<...> struct h1 { ... };`). Each tag takes 0 or more type/ 88 | non-type template parameters. Template parameters can be HTML attributes 89 | (e.g. `"img`) or an arbitrarily long list of 90 | other element types, which can themselves hold other types as child nodes 91 | (e.g. `html>, body<...>>`). 92 | 93 | Type safety can be achieved by defining only template parameters that make sense for 94 | a tag (e.g. `` is a self-closing tag, so it would not make sense for it to accept a 95 | template parameter pack of child nodes). Using inheritance and 96 | `static_assert`, along with "phantom" types (e.g. `img` inherits from an empty struct 97 | named `body_element_tag`), ensures that the tags make semantic sense as children 98 | of a given node. In this way, HTML can be given a degree of type-checking. 99 | 100 | The output text is assembled by pre-order traversing the tree of types, calling each type's 101 | constructor recursively. Each element adds its opening tag (e.g. ``) to a string 102 | that is then passed by reference to each child element recursively. Once all children have 103 | added their opening tags, each node adds its closing tag (e.g. ``) and returns from its 104 | constructor. The string is stored in a member of the top-level node (`html`) and can be 105 | printed and/or used like a normal string at runtime. The string is assembled at runtime; 106 | however, the structure of the document is defined at compile-time. 107 | 108 | ### Should I use it 109 | 110 | Probably not. However, I think the type-checking aspect could be useful. I haven't added all HTML tags, 111 | but in theory this library could be extended in such a way that you could write HTML 112 | with somewhat strong typing, which might be useful for ensuring HTML standards conformance. 113 | 114 | Hope this project is interesting (and concerning) to you! 115 | -------------------------------------------------------------------------------- /html++.h: -------------------------------------------------------------------------------- 1 | #pragma once 2 | #include 3 | #include 4 | #include 5 | 6 | #define STATIC_ASSERT_CHILDREN_ARE_VALID(BASE_TAG, TAG_NAME) \ 7 | static_assert(((std::is_base_of_v || std::is_same_v) && ...), \ 8 | "<" #TAG_NAME "> must contain type 'void' or an element that is a subclass of " #BASE_TAG " for all template parameters"); 9 | 10 | // Not yet implemented in GCC 9 std lib; will be in C++20, but I had 11 | // to add it here for now 12 | template< class InputIt, class Size, class OutputIt> 13 | constexpr OutputIt copy_n(InputIt first, Size count, OutputIt result) 14 | { 15 | if (count > 0) { 16 | *result++ = *first; 17 | for (Size i = 1; i < count; ++i) { 18 | *result++ = *++first; 19 | } 20 | } 21 | return result; 22 | } 23 | 24 | constexpr void add_indent(std::string &page_content, unsigned indent) 25 | { 26 | for(unsigned i = 0; i < indent; ++i) { 27 | page_content += " "; 28 | } 29 | } 30 | 31 | template 32 | struct StringLiteral { 33 | constexpr StringLiteral(const char (&str)[N]) 34 | { 35 | copy_n(str, N, value); 36 | } 37 | 38 | char value[N]{}; 39 | constexpr bool empty() const { return N == 0; } 40 | constexpr const char* c_str() const { return &value[0]; } 41 | }; 42 | 43 | 44 | struct add_tag { 45 | add_tag(std::string &page_content_, const char *tag_, unsigned indent_ = 0) 46 | : add_tag(page_content_, tag_, indent_, false) 47 | {} 48 | 49 | template 50 | add_tag(std::string &page_content_, const char *tag_, unsigned indent_, 51 | bool is_self_closing_, Attributes... attributes) 52 | : page_content(page_content_), tag(tag_), indent(indent_), 53 | is_self_closing(is_self_closing_) 54 | { 55 | static_assert((std::is_convertible_v && ...), 56 | "HTML attributes must be string literals"); 57 | add_indent(page_content, indent); 58 | page_content += '<'; 59 | page_content += tag; 60 | auto add_attributes = [this](const auto each) { 61 | if(each != nullptr && each[0] != '\0') { 62 | page_content += ' '; 63 | page_content += each; 64 | } 65 | }; 66 | 67 | (add_attributes(attributes), ...); 68 | page_content += ">\n"; 69 | } 70 | 71 | ~add_tag() 72 | { 73 | if (!is_self_closing) { 74 | add_indent(page_content, indent); 75 | page_content += "\n"; 78 | } 79 | } 80 | private: 81 | std::string &page_content; 82 | const char *tag; 83 | unsigned indent; 84 | bool is_self_closing; 85 | }; 86 | 87 | 88 | // Identifies the HTML tag 89 | struct head_tag {}; 90 | // Identifies an HTML tag that can legally be within 91 | struct head_element_tag {}; 92 | 93 | template 94 | struct head : head_tag { 95 | STATIC_ASSERT_CHILDREN_ARE_VALID(head_element_tag, head) 96 | explicit head(std::string &page_content) 97 | { 98 | add_tag scope_guard(page_content, "head", 1); 99 | (Children(page_content, 2), ...); 100 | } 101 | }; 102 | 103 | 104 | template 105 | struct title : head_element_tag { 106 | title(std::string &page_content, unsigned indent) 107 | { 108 | add_tag scope_guard(page_content, "title", indent); 109 | add_indent(page_content, indent + 1); 110 | page_content += Content.c_str(); 111 | page_content += '\n'; 112 | } 113 | }; 114 | 115 | 116 | // Identifies the HTML tag 117 | struct body_tag {}; 118 | // Identifies an HTML tag that can legally be within 119 | struct body_element_tag {}; 120 | 121 | template 122 | struct body : body_tag { 123 | STATIC_ASSERT_CHILDREN_ARE_VALID(body_element_tag, body) 124 | explicit body(std::string &page_content) 125 | { 126 | add_tag scope_guard(page_content, "body", 1); 127 | (Children(page_content, 2), ...); 128 | } 129 | }; 130 | 131 | 132 | template 133 | struct html { 134 | static_assert(std::is_base_of_v || std::is_same_v, 135 | " must contain type 'void' or type 'head' as its first template parameter"); 136 | static_assert(std::is_base_of_v || std::is_same_v, 137 | " must contain type 'void' or type 'body' as its second template parameter"); 138 | html() 139 | { 140 | add_tag scope_guard(content, "html"); 141 | if constexpr(!std::is_same_v) { 142 | head_{content}; 143 | } 144 | 145 | if constexpr(!std::is_same_v) { 146 | body_{content}; 147 | } 148 | } 149 | 150 | std::string content; 151 | }; 152 | 153 | // Form 5: body_element with attributes but no content 154 | template 155 | struct img : body_element_tag { 156 | img(std::string &page_content, unsigned indent) 157 | { 158 | add_tag scope_guard(page_content, "img", indent, true, Src.value, Alt.value, Width.value); 159 | } 160 | }; 161 | 162 | // Form 4: body_element with no attributes and no content 163 | struct br : body_element_tag { 164 | br(std::string &page_content, unsigned indent) 165 | { 166 | add_tag scope_guard(page_content, "br", indent, true); 167 | } 168 | }; 169 | 170 | // Form 3: body_element with attributes and content 171 | template 172 | struct a : body_element_tag { 173 | a(std::string &page_content, unsigned indent) 174 | { 175 | add_tag scope_guard(page_content, "a", indent, false, Href.value); 176 | if constexpr (!Content.empty()) { 177 | add_indent(page_content, indent + 1); 178 | page_content += Content.c_str(); 179 | page_content += '\n'; 180 | } 181 | (Children(page_content, indent + 1), ...); 182 | } 183 | }; 184 | 185 | 186 | // Form 2: body_element with no content but children 187 | template 188 | struct div_ : body_element_tag { 189 | STATIC_ASSERT_CHILDREN_ARE_VALID(body_element_tag, div) 190 | div_(std::string &page_content, unsigned indent) 191 | { 192 | add_tag scope_guard(page_content, "div", indent); 193 | (Children(page_content, indent + 1), ...); 194 | } 195 | }; 196 | 197 | // Form 1: body_element with content and children 198 | template 199 | struct p : body_element_tag { 200 | STATIC_ASSERT_CHILDREN_ARE_VALID(body_element_tag, p) 201 | p(std::string &page_content, unsigned indent) 202 | { 203 | add_tag scope_guard(page_content, "p", indent); 204 | if constexpr (!Content.empty()) { 205 | add_indent(page_content, indent + 1); 206 | page_content += Content.c_str(); 207 | page_content += '\n'; 208 | } 209 | (Children(page_content, indent + 1), ...); 210 | } 211 | }; 212 | 213 | template 214 | struct h1 : body_element_tag { 215 | STATIC_ASSERT_CHILDREN_ARE_VALID(body_element_tag, h1) 216 | h1(std::string &page_content, unsigned indent) 217 | { 218 | add_tag scope_guard(page_content, "h1", indent); 219 | if constexpr (!Content.empty()) { 220 | add_indent(page_content, indent + 1); 221 | page_content += Content.c_str(); 222 | page_content += '\n'; 223 | } 224 | (Children(page_content, indent + 1), ...); 225 | } 226 | }; 227 | 228 | template 229 | struct h2 : body_element_tag { 230 | STATIC_ASSERT_CHILDREN_ARE_VALID(body_element_tag, h2) 231 | h2(std::string &page_content, unsigned indent) 232 | { 233 | add_tag scope_guard(page_content, "h2", indent); 234 | if constexpr (!Content.empty()) { 235 | add_indent(page_content, indent + 1); 236 | page_content += Content.c_str(); 237 | page_content += '\n'; 238 | } 239 | (Children(page_content, indent + 1), ...); 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No Surrender of Others' Freedom. 529 | 530 | If conditions are imposed on you (whether by court order, agreement or 531 | otherwise) that contradict the conditions of this License, they do not 532 | excuse you from the conditions of this License. If you cannot convey a 533 | covered work so as to satisfy simultaneously your obligations under this 534 | License and any other pertinent obligations, then as a consequence you may 535 | not convey it at all. For example, if you agree to terms that obligate you 536 | to collect a royalty for further conveying from those to whom you convey 537 | the Program, the only way you could satisfy both those terms and this 538 | License would be to refrain entirely from conveying the Program. 539 | 540 | 13. Remote Network Interaction; Use with the GNU General Public License. 541 | 542 | Notwithstanding any other provision of this License, if you modify the 543 | Program, your modified version must prominently offer all users 544 | interacting with it remotely through a computer network (if your version 545 | supports such interaction) an opportunity to receive the Corresponding 546 | Source of your version by providing access to the Corresponding Source 547 | from a network server at no charge, through some standard or customary 548 | means of facilitating copying of software. This Corresponding Source 549 | shall include the Corresponding Source for any work covered by version 3 550 | of the GNU General Public License that is incorporated pursuant to the 551 | following paragraph. 552 | 553 | Notwithstanding any other provision of this License, you have 554 | permission to link or combine any covered work with a work licensed 555 | under version 3 of the GNU General Public License into a single 556 | combined work, and to convey the resulting work. The terms of this 557 | License will continue to apply to the part which is the covered work, 558 | but the work with which it is combined will remain governed by version 559 | 3 of the GNU General Public License. 560 | 561 | 14. Revised Versions of this License. 562 | 563 | The Free Software Foundation may publish revised and/or new versions of 564 | the GNU Affero General Public License from time to time. Such new versions 565 | will be similar in spirit to the present version, but may differ in detail to 566 | address new problems or concerns. 567 | 568 | Each version is given a distinguishing version number. If the 569 | Program specifies that a certain numbered version of the GNU Affero General 570 | Public License "or any later version" applies to it, you have the 571 | option of following the terms and conditions either of that numbered 572 | version or of any later version published by the Free Software 573 | Foundation. If the Program does not specify a version number of the 574 | GNU Affero General Public License, you may choose any version ever published 575 | by the Free Software Foundation. 576 | 577 | If the Program specifies that a proxy can decide which future 578 | versions of the GNU Affero General Public License can be used, that proxy's 579 | public statement of acceptance of a version permanently authorizes you 580 | to choose that version for the Program. 581 | 582 | Later license versions may give you additional or different 583 | permissions. However, no additional obligations are imposed on any 584 | author or copyright holder as a result of your choosing to follow a 585 | later version. 586 | 587 | 15. Disclaimer of Warranty. 588 | 589 | THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY 590 | APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT 591 | HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY 592 | OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, 593 | THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 594 | PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM 595 | IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF 596 | ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 597 | 598 | 16. Limitation of Liability. 599 | 600 | IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING 601 | WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS 602 | THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY 603 | GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE 604 | USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF 605 | DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD 606 | PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), 607 | EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF 608 | SUCH DAMAGES. 609 | 610 | 17. Interpretation of Sections 15 and 16. 611 | 612 | If the disclaimer of warranty and limitation of liability provided 613 | above cannot be given local legal effect according to their terms, 614 | reviewing courts shall apply local law that most closely approximates 615 | an absolute waiver of all civil liability in connection with the 616 | Program, unless a warranty or assumption of liability accompanies a 617 | copy of the Program in return for a fee. 618 | 619 | END OF TERMS AND CONDITIONS 620 | 621 | How to Apply These Terms to Your New Programs 622 | 623 | If you develop a new program, and you want it to be of the greatest 624 | possible use to the public, the best way to achieve this is to make it 625 | free software which everyone can redistribute and change under these terms. 626 | 627 | To do so, attach the following notices to the program. It is safest 628 | to attach them to the start of each source file to most effectively 629 | state the exclusion of warranty; and each file should have at least 630 | the "copyright" line and a pointer to where the full notice is found. 631 | 632 | 633 | Copyright (C) 634 | 635 | This program is free software: you can redistribute it and/or modify 636 | it under the terms of the GNU Affero General Public License as published 637 | by the Free Software Foundation, either version 3 of the License, or 638 | (at your option) any later version. 639 | 640 | This program is distributed in the hope that it will be useful, 641 | but WITHOUT ANY WARRANTY; without even the implied warranty of 642 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 643 | GNU Affero General Public License for more details. 644 | 645 | You should have received a copy of the GNU Affero General Public License 646 | along with this program. If not, see . 647 | 648 | Also add information on how to contact you by electronic and paper mail. 649 | 650 | If your software can interact with users remotely through a computer 651 | network, you should also make sure that it provides a way for users to 652 | get its source. For example, if your program is a web application, its 653 | interface could display a "Source" link that leads users to an archive 654 | of the code. There are many ways you could offer source, and different 655 | solutions will be better for different programs; see section 13 for the 656 | specific requirements. 657 | 658 | You should also get your employer (if you work as a programmer) or school, 659 | if any, to sign a "copyright disclaimer" for the program, if necessary. 660 | For more information on this, and how to apply and follow the GNU AGPL, see 661 | . 662 | --------------------------------------------------------------------------------