7cafe04e0d
## Abstract This pull request implements [P3029R1](https://wg21.link/P3029R1). The paper discusses the current behavior of `mdspan`'s most common pointer-indices CTAD, where the `Extents` template parameter is deduced as `dextents` (dynamic extents), even when passing compile-time constant values. The author believes this behavior is suboptimal, as it doesn't take advantage of the compile-time information. The proposed change suggests deducing static extents if `integral_constant`-like constants are passed, resulting in more intuitive syntax and less error-prone code. ## Reference - [P3029R1](https://wg21.link/P3029R1) - [Draft C++ Standard: [span.syn]](https://eel.is/c++draft/span.syn) - [Draft C++ Standard: [mdspan.syn]](https://eel.is/c++draft/mdspan.syn)
127 lines
3.1 KiB
C++
127 lines
3.1 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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// UNSUPPORTED: c++03, c++11, c++14, c++17
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// <span>
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// template<class It, class EndOrSize>
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// span(It, EndOrSize) -> span<remove_reference_t<iter_reference_t<_It>>>;
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//
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// template<class T, size_t N>
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// span(T (&)[N]) -> span<T, N>;
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//
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// template<class T, size_t N>
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// span(array<T, N>&) -> span<T, N>;
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//
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// template<class T, size_t N>
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// span(const array<T, N>&) -> span<const T, N>;
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//
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// template<class R>
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// span(R&&) -> span<remove_reference_t<ranges::range_reference_t<R>>>;
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#include <span>
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#include <array>
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#include <cassert>
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#include <iterator>
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#include <memory>
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#include <string>
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#include <type_traits>
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#include "test_macros.h"
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void test_iterator_sentinel() {
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int arr[] = {1, 2, 3};
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{
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std::span s{std::begin(arr), std::end(arr)};
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ASSERT_SAME_TYPE(decltype(s), std::span<int>);
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assert(s.size() == std::size(arr));
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assert(s.data() == std::data(arr));
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}
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{
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std::span s{std::begin(arr), 3};
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ASSERT_SAME_TYPE(decltype(s), std::span<int>);
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assert(s.size() == std::size(arr));
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assert(s.data() == std::data(arr));
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}
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#if _LIBCPP_STD_VER >= 26
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// P3029R1: deduction from `integral_constant`
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{
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std::span s{std::begin(arr), std::integral_constant<size_t, 3>{}};
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ASSERT_SAME_TYPE(decltype(s), std::span<int, 3>);
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assert(s.size() == std::size(arr));
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assert(s.data() == std::data(arr));
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}
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#endif
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}
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void test_c_array() {
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{
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int arr[] = {1, 2, 3};
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std::span s{arr};
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ASSERT_SAME_TYPE(decltype(s), std::span<int, 3>);
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assert(s.size() == std::size(arr));
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assert(s.data() == std::data(arr));
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}
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{
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const int arr[] = {1,2,3};
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std::span s{arr};
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ASSERT_SAME_TYPE(decltype(s), std::span<const int, 3>);
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assert(s.size() == std::size(arr));
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assert(s.data() == std::data(arr));
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}
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}
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void test_std_array() {
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{
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std::array<double, 4> arr = {1.0, 2.0, 3.0, 4.0};
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std::span s{arr};
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ASSERT_SAME_TYPE(decltype(s), std::span<double, 4>);
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assert(s.size() == arr.size());
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assert(s.data() == arr.data());
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}
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{
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const std::array<long, 5> arr = {4, 5, 6, 7, 8};
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std::span s{arr};
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ASSERT_SAME_TYPE(decltype(s), std::span<const long, 5>);
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assert(s.size() == arr.size());
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assert(s.data() == arr.data());
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}
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}
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void test_range_std_container() {
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{
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std::string str{"ABCDE"};
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std::span s{str};
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ASSERT_SAME_TYPE(decltype(s), std::span<char>);
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assert(s.size() == str.size());
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assert(s.data() == str.data());
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}
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{
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const std::string str{"QWERTYUIOP"};
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std::span s{str};
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ASSERT_SAME_TYPE(decltype(s), std::span<const char>);
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assert(s.size() == str.size());
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assert(s.data() == str.data());
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}
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}
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int main(int, char**)
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{
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test_iterator_sentinel();
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test_c_array();
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test_std_array();
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test_range_std_container();
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return 0;
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}
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