RetroSearch Browse

Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../container/span/deduction_guides.html below:

deduction guides for std::span - cppreference.com

(1) (since C++20)
(until C++26) (since C++26) template< class T, std::size_t N > span( T (&)[N] ) -> span<T, N>; (2) (since C++20) (3) (since C++20) (4) (since C++20) (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

#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 â sizeof â extent\n"
                     "ââââââ¼âââââââââ¼ââââââââ\n";
        return;
    }
    std::cout << std::setw(4) << rem << " â " << std::setw(6) << size_of << " â ";
    if (extent == std::dynamic_extent)
        std::cout << "dynamic";
    else
        std::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 > 202302L
    std::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'
 
    const std::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 â sizeof â extent
ââââââ¼âââââââââ¼ââââââââ
  s1 â     16 â dynamic
  s2 â     16 â dynamic
  s3 â      8 â 2
  s4 â      8 â 5
  s5 â     16 â dynamic
  s6 â      8 â 3
  s7 â      8 â 3
  s8 â     16 â dynamic

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4