├── .gitignore ├── .gitattributes ├── .editorconfig ├── CMakeLists.txt ├── README.md ├── include └── nrr_enumerate │ └── nrr_enumerate.h └── LICENSE.txt /.gitignore: -------------------------------------------------------------------------------- 1 | build/ 2 | install/ 3 | -------------------------------------------------------------------------------- /.gitattributes: -------------------------------------------------------------------------------- 1 | # Don't mess with my line endings (treat all files as binary) 2 | * -text 3 | -------------------------------------------------------------------------------- /.editorconfig: -------------------------------------------------------------------------------- 1 | root=true 2 | 3 | [*] 4 | end_of_line=lf 5 | insert_final_newline=true 6 | charset=utf-8 7 | indent_style=space 8 | indent_size=4 9 | trim_trailing_whitespace=true 10 | -------------------------------------------------------------------------------- /CMakeLists.txt: -------------------------------------------------------------------------------- 1 | cmake_minimum_required(VERSION 3.15) 2 | project(nrr_enumerate LANGUAGES CXX) 3 | 4 | add_library(${PROJECT_NAME} INTERFACE) 5 | 6 | include(GNUInstallDirs) 7 | 8 | target_include_directories( 9 | ${PROJECT_NAME} INTERFACE 10 | $ 11 | $) 12 | 13 | target_compile_features( 14 | ${PROJECT_NAME} INTERFACE cxx_std_17) 15 | 16 | install( 17 | TARGETS ${PROJECT_NAME} 18 | EXPORT ${PROJECT_NAME}-config) 19 | 20 | install( 21 | EXPORT ${PROJECT_NAME}-config 22 | NAMESPACE ${PROJECT_NAME}:: 23 | DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}) 24 | 25 | install( 26 | DIRECTORY ${CMAKE_CURRENT_LIST_DIR}/include/${PROJECT_NAME}/ 27 | DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/${PROJECT_NAME}) 28 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # nrr_enumerate 2 | Python-like 'enumerate' for C++ 3 | 4 | Python and some other languages have a handy built-in function called [`enumerate()`](https://docs.python.org/3/library/functions.html?highlight=enumerate#enumerate), which lets you iterate over an object (e.g. a list) and have access to both the index and the item in each iteration. This header gives a C++17/20 implementation of the same idea. Use it like: 5 | 6 | ```cpp 7 | std::vector things; 8 | ... 9 | for (auto [i, thing] : enumerate(things)) 10 | { 11 | // i gets the index and thing gets the Thing in each iteration 12 | } 13 | ``` 14 | 15 | Iterating over `things` itself would give you `thing`, but not `i`, and there are plenty of situations where you want both. See the [accompanying blog post](http://reedbeta.com/blog/python-like-enumerate-in-cpp17/) for more info. 16 | 17 | There's also a const version, `cenumerate()`, which iterates the given object as const. (Sadly, using `const auto [i, thing]` doesn't actually do the job, because of reasons.) 18 | -------------------------------------------------------------------------------- /include/nrr_enumerate/nrr_enumerate.h: -------------------------------------------------------------------------------- 1 | // nrr_enumerate: iterate indices and items at the same time 2 | // See http://www.reedbeta.com/blog/python-like-enumerate-in-cpp17/ 3 | 4 | // Copyright 2021 Nathan Reed 5 | // 6 | // Licensed under the Apache License, Version 2.0 (the "License"); 7 | // you may not use this file except in compliance with the License. 8 | // You may obtain a copy of the License at 9 | // 10 | // http://www.apache.org/licenses/LICENSE-2.0 11 | // 12 | // Unless required by applicable law or agreed to in writing, software 13 | // distributed under the License is distributed on an "AS IS" BASIS, 14 | // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 | // See the License for the specific language governing permissions and 16 | // limitations under the License. 17 | 18 | #pragma once 19 | #include 20 | #include 21 | 22 | // Hide requires clauses from pre-C++20 compilers and MSVC Intellisense 23 | #if (__cplusplus >= 201709L) || (defined(_MSVC_LANG) && (_MSVC_LANG >= 201705L)) 24 | # define NRR_REQUIRES(...) requires(__VA_ARGS__) 25 | #else 26 | # define NRR_REQUIRES(...) 27 | #endif 28 | 29 | namespace nrr 30 | { 31 | template 32 | NRR_REQUIRES(requires { std::begin(std::declval()); std::end(std::declval()); }) 33 | constexpr auto enumerate(T&& iterable) 34 | { 35 | struct iterator 36 | { 37 | size_t i; 38 | decltype(std::begin(iterable)) iter; 39 | bool operator != (const iterator & other) const { return iter != other.iter; } 40 | void operator ++ () { ++i; ++iter; } 41 | auto operator * () const { return std::tie(i, *iter); } 42 | }; 43 | struct iterable_wrapper 44 | { 45 | T iterable; 46 | auto begin() { return iterator{ 0, std::begin(iterable) }; } 47 | auto end() { return iterator{ 0, std::end(iterable) }; } 48 | }; 49 | return iterable_wrapper{ std::forward(iterable) }; 50 | } 51 | 52 | template 53 | NRR_REQUIRES(requires { std::cbegin(std::declval()); std::cend(std::declval()); }) 54 | constexpr auto cenumerate(T&& iterable) 55 | { 56 | struct iterator 57 | { 58 | size_t i; 59 | decltype(std::cbegin(iterable)) iter; 60 | bool operator != (const iterator & other) const { return iter != other.iter; } 61 | void operator ++ () { ++i; ++iter; } 62 | auto operator * () const { return std::tie(i, *iter); } 63 | }; 64 | struct iterable_wrapper 65 | { 66 | T iterable; 67 | auto begin() { return iterator{ 0, std::cbegin(iterable) }; } 68 | auto end() { return iterator{ 0, std::cend(iterable) }; } 69 | }; 70 | return iterable_wrapper{ std::forward(iterable) }; 71 | } 72 | } // namespace nrr 73 | 74 | #undef NRR_REQUIRES 75 | -------------------------------------------------------------------------------- /LICENSE.txt: -------------------------------------------------------------------------------- 1 | 2 | Apache License 3 | Version 2.0, January 2004 4 | http://www.apache.org/licenses/ 5 | 6 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 7 | 8 | 1. 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