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std::experimental::optional::operator=

From cppreference.com
optional& operator=( std::nullopt_t );
(1) (library fundamentals TS)
optional& operator=( const optional& other );
(2) (library fundamentals TS)
optional& operator=( optional&& other );
(3) (library fundamentals TS)
template< class U >
optional& operator=( U&& value );
(4) (library fundamentals TS)

Assigns contents to the contained value.

1) If *this is in engaged state before the call, the contained value is destroyed by calling its destructor. *this is in disengaged state after the call.
2-3) Assigns the state of other.
* If both *this and other are in disengaged states, the function has no effect.
* If *this is in engaged state, but other is not, then the contained value is destroyed by calling its destructor. *this is in disengaged state after the call.
* If other is in engaged state, then depending on whether *this is in engaged state, the contained value is either direct-constructed or assigned the contained value of other. The contained value is either copied (2), or moved (3).
4) Depending on whether *this is in engaged state before the call, the contained value is either direct-constructed from value or assigned value. T must be constructible and assignable from U, i.e. the following must hold: std::is_constructible<T,U>::value == true && std::is_assignable<T,U>::value == true

Contents

[edit] Parameters

other - another optional object whose contained value to assign
value - value to assign to the contained value
Type requirements
-
T must meet the requirements of CopyAssignable and CopyConstructible in order to use overload (2).
-
T must meet the requirements of MoveAssignable and MoveConstructible in order to use overload (3).

[edit] Return value

*this

[edit] Exceptions

1)
noexcept specification:  
noexcept
  
2-4) Throws any exception thrown by the constructor or assignment operator of T. If an exception is thrown, the initialization state of *this (and of other in case of (2) ) is unchanged, i.e. if the object was in engaged state, it is left in engaged state, and the other way round. The contents of value and the contained values of *this and other depend on the exception safety guarantees of the operation from which the exception originates (copy-constructor, move-assignment, etc.).
3) Throws any exception thrown by the constructor or assignment operator T. Has the following noexcept declaration:
noexcept specification:  (since C++11)

[edit] See also

constructs the contained value in-place
(public member function) [edit]