W3cubDocs

/C++

std::ranges::views::all, std::ranges::views::all_t

Defined in header <ranges> 
inline constexpr /* unspecified */ all = /* unspecified */;
 (1) (since C++20) 
template <ranges::viewable_range R>
using all_t = decltype(views::all(std::declval<R>()));
 (2) (since C++20)
1) A range adaptor object (also a range adaptor closure object) that returns a view that includes all elements of its range argument.

The expression views::all(e) is expression-equivalent (has the same effect) to:

  • Implicitly converting e to a std::decay_t<decltype((e))> prvalue, if the result type models view.
  • Otherwise, std::ranges::ref_view{e} if that expression is well-formed.
  • Otherwise, std::ranges::owning_view{e}.
2) Calculates the suitable view type of a viewable_range type.

Expression-equivalent

Expression e is expression-equivalent to expression f, if.

  • e and f have the same effects, and
  • either both are constant subexpressions or else neither is a constant subexpression, and
  • either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

Example 

#include <ranges>
#include <vector>
#include <iostream>
#include <type_traits>
 
int main()
{
    std::vector<int> v{0,1,2,3,4,5};
    for(int n : std::views::all(v) | std::views::take(2) ) {
        std::cout << n << ' ';
    }
 
    static_assert(std::is_same<
        decltype(std::views::single(42)),
        std::ranges::single_view<int>
        >{});
 
    static_assert(std::is_same<
        decltype(std::views::all(v)),
        std::ranges::ref_view<std::vector<int, std::allocator<int>>>
        >{});
 
    int a[]{1,2,3,4};
    static_assert(std::is_same<
        decltype(std::views::all(a)),
        std::ranges::ref_view<int [4]>
        >{});
 
    static_assert(std::is_same<
        decltype(std::ranges::subrange{std::begin(a)+1, std::end(a)-1}),
        std::ranges::subrange<int*, int*, std::ranges::subrange_kind(1)>
        >{});
}

Output:

0 1

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P2415R2 C++20 views::all returned a subrange for a non-view rvalue range returns a owning_view for it

See also

(C++20)
 an empty view with no elements
(class template) (variable template)
(C++20)
 a view that contains a single element of a specified value
(class template) (customization point object)
(C++20)
 a view with unique ownership of some range
(class template)

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/ranges/all_view