std::experimental::optional::optional
From cppreference.com
< cpp | experimental | optional
constexpr optional();
constexpr optional( std::experimental::nullopt_t ); |
(1) | (library fundamentals TS) |
optional( const optional& other );
|
(2) | (library fundamentals TS) |
optional( optional&& other );
|
(3) | (library fundamentals TS) |
constexpr optional( const T& value );
|
(4) | (library fundamentals TS) |
constexpr optional( T&& value );
|
(5) | (library fundamentals TS) |
template< class... Args >
constexpr explicit optional( std::experimental::in_place_t, Args&&... args ); |
(6) | (library fundamentals TS) |
template< class U, class... Args >
constexpr explicit optional( std::experimental::in_place_t, |
(7) | (library fundamentals TS) |
Constructs a new optional
object.
1) Constructs the object that does not contain a value.
2) Copy constructor: If
other
contains a value, initializes the contained value as if direct-initializing (but not direct-list-initializing) an object of type T
with the expression *other. If other
does not contain a value, constructs an object that does not contain a value.
3) Move constructor: If
other
contains a value, initializes the contained value as if direct-initializing (but not direct-list-initializing) an object of type T
with the expression std::move(*other) and does not make other
empty: a moved-from optional still contains a value, but the value itself is moved from. If other
does not contain a value, constructs an object that does not contain a value.
4) Constructs an optional object that contains a value, initialized as if direct-initializing (but not direct-list-initializing) an object of type
T
with the expression value. This constructor is constexpr
if the constructor of T
selected by direct-initialization is constexpr
.
5) Constructs an optional object that contains a value, initialized as if direct-initializing (but not direct-list-initializing) an object of type
T
with the expression std::move(value). This constructor is constexpr
if the constructor of T
selected by direct-initialization is constexpr
.
6) Constructs an optional object that contains a value, initialized as if direct-initializing (but not direct-list-initializing) an object of type
T
from the arguments std::forward<Args>(args)...
7) Constructs an optional object that contains a value, initialized as if direct-initializing (but not direct-list-initializing) an object of type
T
from the arguments ilist, std::forward<Args>(args).... The function does not participate in the overload resolution if std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value != true
Contents |
[edit] Parameters
other | - | another optional object whose contained value to copy
|
value | - | value to initialize the contained value with |
args... | - | arguments to initialize the contained value with |
ilist | - | initializer list to initialize the contained value with |
Type requirements | ||
-
T must meet the requirements of CopyConstructible in order to use overloads (2,4).
|
||
-
T must meet the requirements of MoveConstructible in order to use overloads (3,5).
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[edit] Exceptions
1)
noexcept specification:
noexcept
2) Throws any exception thrown by the constructor of
T
.
3) Throws any exception thrown by the constructor of
T
. Has the following noexcept
declaration:
noexcept specification:
.noexcept(std::is_nothrow_move_constructible<T>::value)
4-7) Throws any exception thrown by the constructor of
T
.[edit] Example
Run this code
#include <experimental/optional> #include <iostream> #include <string> int main() { std::experimental::optional<int> o1, // empty o2 = 1, // init from rvalue o3 = o2; // copy-constructor std::experimental::optional<std::string> o4(std::experimental::in_place, {'a', 'b', 'c'}); std::cout << *o2 << ' ' << *o3 << ' ' << *o4 << '\n'; }
Output:
1 1 abc
[edit] See also
creates an optional object (function template) |