std::ranges:: views:: empty, std::ranges:: empty_view
|
Defined in header
<ranges>
|
||
|
template
<
class
T
>
requires
std::
is_object_v
<
T
>
|
(1) | (since C++20) |
|
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 |
|
|
(C++23)
|
returns a constant iterator to the beginning of the range.
(public member function of
std::ranges::view_interface<D>
)
|
|
(C++23)
|
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>
)
|
|
returns the first element in the derived view. Provided if it satisfies
forward_range
.
(public member function of
std::ranges::view_interface<D>
)
|
|
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>
)
|
|
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>
)
|
|
std::ranges::empty_view:: begin
|
static
constexpr
T
*
begin
(
)
noexcept
{
return
nullptr
;
}
|
(since C++20) | |
empty_view
does not reference any element.
std::ranges::empty_view:: end
|
static
constexpr
T
*
end
(
)
noexcept
{
return
nullptr
;
}
|
(since C++20) | |
empty_view
does not reference any element.
std::ranges::empty_view:: data
|
static
constexpr
T
*
data
(
)
noexcept
{
return
nullptr
;
}
|
(since C++20) | |
empty_view
does not reference any element.
std::ranges::empty_view:: size
|
static
constexpr
std::
size_t
size
(
)
noexcept
{
return
0
;
}
|
(since C++20) | |
empty_view
is always empty.
std::ranges::empty_view:: empty
|
static
constexpr
bool
empty
(
)
noexcept
{
return
true
;
}
|
(since C++20) | |
empty_view
is always empty.
Helper templates
|
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
is always empty.
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
|
(C++17)
|
a wrapper that may or may not hold an object
(class template) |
a
view
that contains a single element of a specified value
(class template) (customization point object) |
|
|
(C++20)
|
a
view
that includes all elements of a
range
(alias template) (range adaptor object) |
|
(C++20)
|
a
view
of the elements of some other
range
(class template) |