std::ranges:: ref_view
|
Defined in header
<ranges>
|
||
|
template
<
ranges::
range
R
>
requires
std::
is_object_v
<
R
>
|
(since C++20) | |
ref_view
is a
view
of the elements of some other
range
. It wraps a reference to that
range
.
Data members
| Member name | Definition |
r_
(private)
|
A pointer of type
R*
to the underlying range.
( exposition-only member object* ) |
Member functions
constructs a
ref_view
that references to the given range
(public member function) |
|
|
returns the references to the referenced range
(public member function) |
|
|
returns the beginning iterator of the referenced range
(public member function) |
|
|
returns the sentinel of the referenced range
(public member function) |
|
|
checks whether the referenced range is empty
(public member function) |
|
returns the size of the referenced
sized_range
(public member function) |
|
returns the pointer to the beginning of the referenced
contiguous_range
(public 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::ref_view:: ref_view
|
template
<
/*different-from*/
<
ref_view
>
T
>
requires
std::
convertible_to
<
T, R
&
>
&&
requires
{
_FUN
(
std::
declval
<
T
>
(
)
)
;
}
|
(since C++20) | |
Initializes
r_
with
std::
addressof
(
static_cast
<
R
&
>
(
std::
forward
<
T
>
(
t
)
)
)
.
/*different-from*/
<
T, U
>
is satisfied if and only if
std::
remove_cvref_t
<
T
>
and
std::
remove_cvref_t
<
U
>
are not the same type, and overloads of
_FUN
are declared as
void
_FUN
(
R
&
)
;
void
_FUN
(
R
&&
)
=
delete
;
.
Parameters
| t | - | range to reference |
std::ranges::ref_view:: base
|
constexpr
R
&
base
(
)
const
;
|
(since C++20) | |
Equivalent to return * r_ ; .
std::ranges::ref_view:: begin
|
constexpr
ranges::
iterator_t
<
R
>
begin
(
)
const
;
|
(since C++20) | |
Equivalent to return ranges:: begin ( * r_ ) ; .
std::ranges::ref_view:: end
|
constexpr
ranges::
sentinel_t
<
R
>
end
(
)
const
;
|
(since C++20) | |
Equivalent to return ranges:: end ( * r_ ) ; .
std::ranges::ref_view:: empty
|
constexpr
bool
empty
(
)
const
requires requires { ranges:: empty ( * r_ ) ; } ; |
(since C++20) | |
Equivalent to return ranges:: empty ( * r_ ) ; .
std::ranges::ref_view:: size
|
constexpr
auto
size
(
)
const
requires ranges:: sized_range < R > ; |
(since C++20) | |
Equivalent to return ranges:: size ( * r_ ) ; .
std::ranges::ref_view:: data
|
constexpr
auto
data
(
)
const
requires ranges:: contiguous_range < R > ; |
(since C++20) | |
Equivalent to return ranges:: data ( * r_ ) ; .
Deduction guides
|
template
<
class
R
>
ref_view ( R & ) - > ref_view < R > ; |
(since C++20) | |
Helper templates
|
template
<
class
T
>
constexpr bool enable_borrowed_range < ranges :: ref_view < T >> = true ; |
(since C++20) | |
This specialization of
std::ranges::enable_borrowed_range
makes
ref_view
satisfy
borrowed_range
.
Example
#include <iostream> #include <ranges> int main() { const std::string s{"cosmos"}; const std::ranges::take_view tv{s, 3}; const std::ranges::ref_view rv{tv}; std::cout << std::boolalpha << "call empty() : " << rv.empty() << '\n' << "call size() : " << rv.size() << '\n' << "call begin() : " << *rv.begin() << '\n' << "call end() : " << *(rv.end() - 1) << '\n' << "call data() : " << rv.data() << '\n' << "call base() : " << rv.base().size() << '\n' // ~> tv.size() << "range-for : "; for (const auto c : rv) std::cout << c; std::cout << '\n'; }
Output:
call empty() : false call size() : 3 call begin() : c call end() : s call data() : cosmos call base() : 3 range-for : cos
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| P2325R3 | C++20 |
default constructor was provided as
view
must be
default_initializable
|
removed along with the requirement |
See also
|
(C++11)
|
CopyConstructible
and
CopyAssignable
reference wrapper
(class template) |
|
(C++20)
|
a
view
with unique ownership of some
range
(class template) |
|
(C++20)
|
a
view
that includes all elements of a
range
(alias template) (range adaptor object) |