std::ranges::views::all, std::ranges::views::all_t
From cppreference.com
Defined in header <ranges>
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inline
constexpr
/* unspecified */ all =
/* unspecified */
;
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(1) | (since C++20) |
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template
<
ranges::viewable_range R >
using all_t = decltype(views:: all ( std::declval <R> ( ) ) ) ; |
(2) | (since C++20) |
1) A RangeAdaptorObject (also a RangeAdaptorClosureObject) that returns a
view that includes all elements of its range
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}
- Otherwise, std::ranges::owning_view{e}
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 error for some move-only views
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it gets well-constrained |
| P2415R2 | C++20 | views::all returned a subrange for a non-view rvalue range
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returns an owning_view for it
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See also
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(C++20)
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an empty view with no elements(class template) (variable template) |
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(C++20)
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a view that contains a single element of a specified value(class template) (customization point object) |
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(C++20)
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a view with unique ownership of some range (class template) |