std::ranges:: views::empty, std::ranges::
Defined in header <ranges>
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template
<
class T>
requires std::is_object_v<T> |
(1) | (since C++20) |
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namespace views {
template
<
class T>
|
(2) | (since C++20) |
view of no elements of a particular type.empty_view.Member functions
begin [static] |
returns nullptr (public static member function) |
end [static] |
returns nullptr (public static member function) |
data [static] |
returns nullptr (public static member function) |
size [static] |
returns 0 (public static member function) |
empty [static] |
returns true (public static member function) |
Inherited from std::ranges::view_interface |
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(C++23)
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returns a constant iterator to the beginning of the range. (public member function of std::ranges::view_interface<D>) |
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(C++23)
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returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D>) |
| returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of std::ranges::view_interface<D>)
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returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>)
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returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range. (public member function of std::ranges::view_interface<D>)
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returns the n
th element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>)
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std::ranges::empty_view::begin
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static
constexpr T* begin(
)
noexcept
{
return nullptr;
}
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(since C++20) | |
empty_view does not reference any element.
std::ranges::empty_view::end
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static
constexpr T* end(
)
noexcept
{
return nullptr;
}
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(since C++20) | |
empty_view does not reference any element.
std::ranges::empty_view::data
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static
constexpr T* data(
)
noexcept
{
return nullptr;
}
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(since C++20) | |
empty_view does not reference any element.
std::ranges::empty_view::size
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static
constexpr
std::size_t size(
)
noexcept
{
return
0
;
}
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(since C++20) | |
empty_view is always empty.
std::ranges::empty_view::empty
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static
constexpr
bool empty(
)
noexcept
{
return
true
;
}
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(since C++20) | |
empty_view is always empty.
Helper templates
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template
<
class T>
constexpr bool ranges::enable_borrowed_range <ranges:: empty_view <T>> = true ; |
(since C++20) | |
This specialization of ranges::enable_borrowed_range makes empty_view satisfy borrowed_range
Notes
Although empty_view obtains front, back, and operator[] member functions from view_interface, calls to them always result in undefined behavior since an empty_view
The inherited operator bool conversion function always returns false
Example
#include <ranges> int main() { namespace ranges = std::ranges; ranges::empty_view<long> e; static_assert(ranges::empty(e)); // uses operator bool static_assert(0 == e.size()); static_assert(nullptr == e.data()); static_assert(nullptr == e.begin()); static_assert(nullptr == e.end()); static_assert(nullptr == e.cbegin()); static_assert(nullptr == e.cend()); }
See also
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(C++17)
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a wrapper that may or may not hold an object (class 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 that includes all elements of a range
(alias template) (range adaptor object) |
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(C++20)
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a view of the elements of some other range (class template) |