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std::ranges::zip_view<Views...>:: size

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Ranges library
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std::ranges::zip_view
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zip_view::size
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constexpr auto size ( )
requires ( ranges:: sized_range < Views > && ... ) ;
(1) (自 C++23 起)
constexpr auto size ( ) const
requires ( ranges:: sized_range < const Views > && ... ) ;
(2) (自 C++23 起)

返回 zip_view 中的元素数量。仅当每个底层（适配的）范围都满足 sized_range 时提供此功能。

相当于： 

return std::apply
(
    [](auto... sizes)
    {
        using CT = /*make-unsigned-like-t*/<std::common_type_t<decltype(sizes)...>>;
        return ranges::min({CT(sizes)...});
    },
    /*tuple-transform*/(ranges::size, views_)
);

目录

参数

(无)

返回值

元素数量，即所有适配的 view 尺寸中的最小值。

示例

运行此代码 
#include <algorithm>
#include <cassert>
#include <deque>
#include <forward_list>
#include <ranges>
#include <vector>
int main()
{
    auto x = std::vector{1, 2, 3, 4, 5};
    auto y = std::deque{'a', 'b', 'c'};
    auto z = std::forward_list{1., 2.};
    auto v1 = std::views::zip(x, y);
    assert(v1.size() == std::min(x.size(), y.size()));
    assert(v1.size() == 3);
    [[maybe_unused]] auto v2 = std::views::zip(x, z);
//  auto sz = v2.size(); // 错误：v2 没有 size() 方法
    static_assert(not std::ranges::sized_range<decltype(z)>);
}

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)