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std::ranges...ewable_range(3)  C++ Standard Libary std::ranges...ewable_range(3)

NAME
     std::ranges::viewable_range - std::ranges::viewable_range

Synopsis
	Defined in header <ranges>
	template< class T >

	concept viewable_range =
	    ranges::range<T> &&
	    ((ranges::view<std::remove_cvref_t<T>> &&
	      std::constructible_from<std::remove_cvref_t<T>,	    T>)       ||
     (since C++20)
	     (!ranges::view<std::remove_cvref_t<T>> &&
	      (std::is_lvalue_reference_v<T> ||

	       (std::movable<std::remove_reference_t<T>> &&
	!/*is-initializer-list*/<T>))));

	The viewable_range concept is a refinement of  range  that  describes  a
     range that can
	be converted into a view through views::all.

	The constant /*is-initializer-list*/<T> is true if and only if
	std::remove_cvref_t<T> is a specialization of std::initializer_list.

Example
     // Run this code

      #include <ranges>
      #include <string>
      #include <vector>

      struct valid_result {};
      struct invalid_result {};

      template <typename T>
      concept valid_viewable_range = std::same_as<T, valid_result>;

      template <typename T>
      concept invalid_viewable_range = std::same_as<T, invalid_result>;

      auto test_viewable_range(std::ranges::viewable_range auto &&) -> valid_re-
     sult;
      auto test_viewable_range(auto&&) -> invalid_result;

      int main()
      {
	  auto il = {1, 2, 3};
	  int arr []{1, 2, 3};
	  std::vector vec{1, 2, 3};
	  std::ranges::ref_view r{arr};
	  std::ranges::owning_view o{std::string("Hello")};

	  static_assert(requires {
	      { test_viewable_range(il) } -> valid_viewable_range;
	      { test_viewable_range(std::move(il)) } -> invalid_viewable_range;
	      { test_viewable_range(arr) } -> valid_viewable_range;
	      { test_viewable_range(std::move(arr)) } -> invalid_viewable_range;
	      { test_viewable_range(vec) } -> valid_viewable_range;
	      { test_viewable_range(std::move(vec)) } -> valid_viewable_range;
	      { test_viewable_range(r) } -> valid_viewable_range;
	      { test_viewable_range(std::move(r)) } -> valid_viewable_range;
	      { test_viewable_range(o) } -> invalid_viewable_range;
	      { test_viewable_range(std::move(o)) } -> valid_viewable_range;
	      {  test_viewable_range(std::ranges::ref_view(o))	} -> valid_view-
     able_range;
	  });
      }

	Defect reports

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

	   DR	  Applied to		 Behavior as published		    Cor-
     rect behavior
	LWG 3481 C++20	    viewable_range accepted an lvalue  of  a	     re-
     jects
			    move-only view
	P2415R2   C++20       viewable_range  only accepted non-view rvalues ac-
     cepts more types
			    that are borrowed_range

See also
	views::all_t a view that includes all elements of a range
	views::all   (alias template) (range adaptor object)
	(C++20)

http://cppreference.com 	   2024.06.10	   std::ranges...ewable_range(3)
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