std::experimental::optional::operator=

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

Experimental libraries

Experimental standard libraries

optional (library fundamentals TS)

any (library fundamentals TS)

basic_string_view (library fundamentals TS)

Polymorphic allocator library (library fundamentals TS)

Filesystem library (filesystem TS)

 

std::experimental::optional

Member functions

optional::optional

optional::~optional

optional::operator=

Observers

optional::operator->optional::operator*

optional::operator bool

optional::value

optional::value_or

Modifiers

optional::emplace

optional::swap

Non-member functions

operator==operator<

make_optional

swap

Helper classes

hash

 

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

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).

Return value

*this

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:  

noexcept(std::is_nothrow_move_assignable<T>::value && std::is_nothrow_move_constructible<T>::value)

See also

emplace

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