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_result;
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_viewable_range;
});
}

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 3481 C++20 viewable_range accepted an lvalue of a rejects
move-only view
P2415R2 C++20 viewable_range only accepted non-view rvalues accepts 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)