std::ranges::views::all,std::ranges::views::all_t(3)

NAME
std::ranges::views::all,std::ranges::views::all_t - std::ranges::views::all,std::ranges::views::all_t

Synopsis
   Defined in header <ranges>
   inline constexpr /* unspecified */ all = /* unspecified */; (1) (since C++20)
   template< ranges::viewable_range R > (2) (since C++20)
   using all_t = decltype(views::all(std::declval<R>()));
   1) A RangeAdaptorObject (also a RangeAdaptorClosureObject) that returns a view that
   includes all elements of its range argument.
   Given an expression e of type R, the expression views::all(e) is
   expression-equivalent to:
     * Implicitly converting e to a std::decay_t<R> prvalue, if std::decay_t<R> 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.

Example
// Run this code
 #include <iostream>
 #include <ranges>
 #include <type_traits>
 #include <vector>
 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 << ' ';
     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
   LWG 3724 C++20 views::all might result in hard it gets well-constrained
                       error for some move-only views
   P2415R2 C++20 views::all returned a subrange for returns an owning_view for it
                       a non-view rvalue range

See also
   ranges::empty_view an empty view with no elements
   views::empty (class template) (variable template)
   (C++20)
   ranges::single_view a view that contains a single element of a specified value
   views::single (class template) (customization point object)
   (C++20)
   ranges::owning_view a view with unique ownership of some range
   (C++20) (class template)