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) |
view
that includes all elements of its range
argument.e
of type R
, the expression views::all(e)
is expression-equivalent to: e
to a std::decay_t<R> prvalue, if std::decay_t<R> models view
. std::ranges::ref_view{e}
if that expression is well-formed. std::ranges::owning_view{e}
.#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 << ' '; 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
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 error for some move-only views | it gets well-constrained |
P2415R2 | C++20 | views::all returned a subrange for a non-view rvalue range | returns an owning_view for it |
(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) |
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