std::ranges::view::all,std::ranges::all_view (3) Linux Manual Page

std::ranges::view::all,std::ranges::all_view – std::ranges::view::all,std::ranges::all_view

Synopsis

template <ViewableRange R>                               (1) (since C++20)

using all_view = decltype(view::all(std::declval<R>()));

namespace view {

    inline constexpr /*unspecified*/ all = /*unspecified*/;  (2) (since C++20)

}

A range adaptor that returns a View that includes all elements of its Range argument.
The expression view::all(E) is expression-equivalent (has the same effect) to:

*decay - copy(E) if the decayed type of E models View.

             *Otherwise,
    std::ranges::ref_view
{
    E
}
if that
    expression is well - formed

                             *Otherwise,
        std::ranges::subrange
    {
        E
    }

Example

// Run this code

#include <ranges>

#include <vector>

#include <iostream>
int main()

{
    std::vector<int> v{0, 1, 2, 3, 4, 5};
    for (int n : std::view::all(v) | std::view::take(2)) {
        std::cout << n << ' ';
    }
}

Output:

  0 1