deduction guides for std::span
From cppreference.com
Defined in header <span> | ||
| (1) | ||
template<class It, class EndOrSize > span( It, EndOrSize )-> span<std::remove_reference_t<std::iter_reference_t<It>>>; | (since C++20) (until C++26) | |
template<class It, class EndOrSize > span( It, EndOrSize )-> span<std::remove_reference_t<std::iter_reference_t<It>>, | (since C++26) | |
template<class T, std::size_t N > span( T (&)[N])-> span<T, N>; | (2) | (since C++20) |
template<class T, std::size_t N > span(std::array<T, N>&)-> span<T, N>; | (3) | (since C++20) |
template<class T, std::size_t N > span(conststd::array<T, N>&)-> span<const T, N>; | (4) | (since C++20) |
template<class R > span( R&&)-> span<std::remove_reference_t<std::ranges::range_reference_t<R>>>; | (5) | (since C++20) |
The following deduction guides are provided for span.
1) Allows the element type to be deduced from the iterator-sentinel pair. It also allows the static extent to be deduced if
EndOrSize satisfies integral-constant-like.(since C++26). This overload participates in overload resolution only if It satisfies contiguous_iterator.2-4) Allows the static extent to be deduced from built-in arrays and std::array.
5) Allows the element type to be deduced from ranges. This overload participates in overload resolution only if
R satisfies contiguous_range.[edit]Example
Run this code
#include <array>#include <cstddef>#include <iomanip>#include <iostream>#include <span>#include <string_view>#include <vector> void print(std::string_view rem ="", std::size_t size_of =0, std::size_t extent =0){if(rem.empty()){std::cout<<"name │ sizeof │ extent\n""─────┼────────┼────────\n";return;}std::cout<<std::setw(4)<< rem <<" │ "<<std::setw(6)<< size_of <<" │ ";if(extent ==std::dynamic_extent)std::cout<<"dynamic";elsestd::cout<< extent;std::cout<<'\n';} int main(){int a[]{1, 2, 3, 4, 5}; print();std::span s1{std::begin(a), std::end(a)};// guide (1) print("s1", sizeof s1, s1.extent); std::span s2{std::begin(a), 3};// guide (1) print("s2", sizeof s2, s2.extent); #if __cplusplus > 202302Lstd::span s3{std::begin(a), std::integral_constant<std::size_t, 2>{}};// guide (1) print("s3", sizeof s3, s3.extent);#endif // C++26 std::span s4{a};// guide (2) print("s4", sizeof s4, s4.extent); std::span<int> s5{a};// does not use a guide, makes a dynamic span print("s5", sizeof s5, s5.extent); std::array arr{6, 7, 8};std::span s6{arr};// guide (3) print("s6", sizeof s6, s6.extent); s6[0]=42;// OK, element_type is 'int' conststd::array arr2{9, 10, 11};std::span s7{arr2};// guide (4) print("s7", sizeof s7, s7.extent);// s7[0] = 42; // Error: element_type is 'const int' std::vector v{66, 69, 99};std::span s8{v};// guide (5) print("s8", sizeof s8, s8.extent);}
Possible output:
name │ sizeof │ extent ─────┼────────┼──────── s1 │ 16 │ dynamic s2 │ 16 │ dynamic s3 │ 8 │ 2 s4 │ 8 │ 5 s5 │ 16 │ dynamic s6 │ 8 │ 3 s7 │ 8 │ 3 s8 │ 16 │ dynamic
