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std::ranges::enumerate_view<V>:: size

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C++
Ranges library
Range adaptors
std::ranges::enumerate_view
Member functions
enumerate_view::size
(C++26)
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constexpr auto size ( ) requires ranges:: sized_range < V > ;
(1) (since C++23)
constexpr auto size ( ) const requires ranges:: sized_range < const V > ;
(2) (since C++23)

Returns the number of elements. Equivalent to return ranges:: size ( base_ ) ; , where base_ is the underlying view.

Contents

Parameters

(none)

Return value

The number of elements.

Example

Run this code 
#include <cassert>
#include <forward_list>
#include <ranges>
#include <string_view>
int main()
{
    constexpr static auto v1 = {1, 2, 3, 4, 5};
    constexpr auto ev1{v1 | std::views::enumerate};
    static_assert(ev1.size() == 5);
    static_assert(std::ranges::sized_range<decltype(v1)>);
    auto v2 = std::forward_list{1, 2, 3, 4, 5};
    auto ev2 {v2 | std::views::enumerate};
    static_assert(not std::ranges::sized_range<decltype(v2)>);
    // auto size = ev2.size(); // Error: v2 is not a sized range
    assert(std::ranges::distance(v2) == 5); // OK, distance does not require sized
                                            // range, but has O(N) complexity here
}

See also

(C++20)
returns an integer equal to the size of a range
(customization point object)
(C++20)
returns a signed integer equal to the size of a range
(customization point object)