decay-copy
|
template
<
class
T
>
typename std:: decay < T > :: type decay - copy ( T && value ) ; |
(since C++11)
(until C++20) ( exposition only* ) |
|
|
template
<
class
T
>
requires
std::
convertible_to
<
T,
std::
decay_t
<
T
>>
|
(since C++20)
( exposition only* ) |
|
Returns std:: forward < T > ( value ) (implicitly converted to the decayed type), a decayed prvalue copy of value .
Parameters
| value | - | the value to be copied |
Return value
A decayed copy of value as a prvalue.
Notes
decay-copy
was introduced by the resolution of
LWG issue 929
. It is initially used in the
concurrency support library
to ensure that arguments are decayed when passing-by-value, and is later used in the
ranges library
.
The language feature
auto
(
x
)
introduced in C++23 also allows decayed copies to be created as prvalues. The only difference is that
decay-copy
always
materializes
value
and produces a copy, while
auto
(
expr
)
is a no-op if
expr
is a prvalue.
All usages of
decay-copy
in the standard library (see below) except
views::all
,
ranges::take_view
and
ranges::drop_view
are replaced with
auto
(
x
)
since C++23.
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 |
decay-copy
was not constrained
|
constrained |
See also
constructs new
thread
object
(public member function of
std::thread
)
|
|
constructs new
jthread
object
(public member function of
std::jthread
)
|
|
|
(C++11)
|
runs a function asynchronously (potentially in a new thread) and returns a
std::future
that will hold the result
(function template) |
|
(C++20)
|
returns an iterator to the beginning of a range
(customization point object) |
|
(C++20)
|
returns a sentinel indicating the end of a range
(customization point object) |
|
(C++20)
|
returns a reverse iterator to a range
(customization point object) |
|
(C++20)
|
returns a reverse end iterator to a range
(customization point object) |
|
(C++20)
|
returns an integer equal to the size of a range
(customization point object) |
|
(C++20)
|
obtains a pointer to the beginning of a contiguous range
(customization point object) |
|
(C++20)
|
a
view
that includes all elements of a
range
(alias template) (range adaptor object) |
|
(C++20)
|
a
view
consisting of the first N elements of another
view
(class template) (range adaptor object) |
|
(C++20)
|
a
view
consisting of elements of another
view
, skipping the first N elements
(class template) (range adaptor object) |