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std::ranges::common_view<V>:: size

From cppreference.net
C++
Ranges library
Range adaptors
std::ranges::common_view
constexpr auto size ( ) requires ranges:: sized_range < V > ;
(1) (自 C++20 起)
constexpr auto size ( ) const requires ranges:: sized_range < const V > ;
(2) (自 C++20 起)

返回元素数量。等价于 return ranges:: size ( base_ ) ; 。

返回值

元素数量。

示例

运行此代码 
#include <ranges>
#include <string_view>
int main()
{
    constexpr static auto v1 = {1, 2, 3, 4, 5};
    constexpr auto common1{v1 | std::views::common};
    static_assert(common1.size() == 5);
    constexpr auto take3{v1 | std::views::reverse | std::views::take(3)};
    constexpr auto common2{take3 | std::views::common};
    static_assert(common2.size() == 3);
    using namespace std::literals;
    constexpr static auto v2 = {"∧"sv, "∨"sv, "∃"sv, "∀"sv};
    static_assert(std::ranges::views::common(v2).size() == 4);
}

参见

(C++20)
返回等于范围大小的整数值
(定制点对象)
(C++20)
返回等于范围大小的有符号整数值
(定制点对象)