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

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.

Parameters

(none).

Return value

The number of elements.

Example

Can be checked online with Compiler Explorer.

#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)

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