deduction guides for std::array
From cppreference.com
C++
Containers library
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std::array
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| Defined in header <array>
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| template< class T, class... U > array( T, U... ) -> array<T, 1 + sizeof...(U)>; |
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One deduction guide is provided for std::array to provide an equivalent of std::experimental::make_array for construction of std::array from a variadic parameter pack.
The program is ill-formed if (std::is_same_v<T, U> && ...) is not true. Note that (std::is_same_v<T, U> && ...) is true when sizeof...(U) is zero.
[edit] Example
Run this code
#include <algorithm> #include <array> #include <cassert> #include <type_traits> int main() { const int x = 10; std::array a{1, 2, 3, 5, x}; / OK, creates std::array<int, 5> assert(a.back() == x); / std::array b{1, 2u}; / Error, all arguments must have the same type / std::array<short> c{3, 2, 1}; / Error, wrong number of template args std::array c{std::to_array<short>({3, 2, 1})}; / C++20 facility assert(std::ranges::equal(c, std::array{3, 2, 1}); static_assert(std::is_same_v<short, decltype(c)::value_type>); }
