std::experimental::optional::optional - cppreference.com (original) (raw)

constexpr optional() noexcept; constexpr optional( std::experimental::nullopt_t ) noexcept; (1) (library fundamentals TS)
optional( const optional& other ); (2) (library fundamentals TS)
optional( optional&& other ) noexcept(/* see below */); (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, std::initializer_list<U> ilist, Args&&... args ); (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.

[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).

[edit] Exceptions

  1. Throws any exception thrown by the constructor of T.

  2. Throws any exception thrown by the constructor of T. Has the following noexcept declaration:

4-7) Throws any exception thrown by the constructor of T.

[edit] Example

[edit] See also