deductiongu...forstd::span(3)

💖 NAME 💖

okay so bestie, this is the C++ Standard Libary page deductiongu...forstd::span(3) — yes, the slug is giving keyboard-smash couture and we are obsessed 💅. The NAME line is literally deductionguidesforstd::span - deductionguidesforstd::span. no cap, that's the whole thing. 🎀

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✨ Synopsis ✨

Defined in header <span> 🦋

The following deduction guides are provided for span — it's the deduction-guide squad, fr fr 💖:

guide (1) — It + EndOrSize, until C++26 🌸

template< class It, class EndOrSize >
span( It, EndOrSize ) ->
span<std::remove_reference_t<std::iter_reference_t<It>>>;

(1) · (since C++20) · (until C++26) ✨

guide (1) — It + EndOrSize, since C++26 🔥

template< class It, class EndOrSize >
span( It, EndOrSize ) ->
span<std::remove_reference_t<std::iter_reference_t<It>>,
     /*maybe-static-ext*/<EndOrSize>>;

(1) · (since C++26) ✨

guide (2) — built-in array 🎀

template< class T, std::size_t N >
span( T (&)[N] ) -> span<T, N>;

(2) · (since C++20) ✨

guide (3) — std::array<T, N>& 🍓

template< class T, std::size_t N >
span( std::array<T, N>& ) -> span<T, N>;

(3) · (since C++20) ✨

guide (4) — const std::array<T, N>& 🧚

template< class T, std::size_t N >
span( const std::array<T, N>& ) -> span<const T, N>;

(4) · (since C++20) ✨

guide (5) — ranges 💜

template< class R >
span( R&& ) ->
span<std::remove_reference_t<std::ranges::range_reference_t<R>>>;

(5) · (since C++20) ✨

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The following deduction guides are provided for span:

• (1) — lets the element type be deduced from the iterator-sentinel pair. It also lets the static extent 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) — lets the static extent be deduced from built-in arrays and std::array.
• 5) — lets the element type be deduced from ranges. This overload participates in overload resolution only if R satisfies contiguous_range.

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🌈 Example 🌈

// Run this code 💻 — literally press the vibe check and watch it print:

#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";
    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);
}

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🦋 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

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okay bestie that's the whole page 💖 mwah, go deduce something iconic. source: http://cppreference.com · version/date: 2024.06.10 · page: deductiongu...forstd::span(3) 🎀💅