23 General utilities library [utilities]

23.6 Optional objects [optional]

23.6.3 Class template optional [optional.optional]

23.6.3.4 Swap [optional.swap]

void swap(optional& rhs) noexcept(see below);
Requires: Lvalues of type T shall be swappable and is_­move_­constructible_­v<T> is true.
Effects: See Table 39.
Table 39optional​::​swap(optional&) effects
*this contains a value
*this does not contain a value
rhs contains a value
calls swap(*(*this), *rhs)
initializes the contained value of *this as if direct-non-list-initializing an object of type T with the expression std​::​move(*rhs), followed by rhs.val->T​::​~T(); postcondition is that *this contains a value and rhs does not contain a value
rhs does not contain a value
initializes the contained value of rhs as if direct-non-list-initializing an object of type T with the expression std​::​move(*(*this)), followed by val->T​::​~T(); postcondition is that *this does not contain a value and rhs contains a value
no effect
Throws: Any exceptions thrown by the operations in the relevant part of Table 39.
Remarks: The expression inside noexcept is equivalent to:
is_nothrow_move_constructible_v<T> && is_nothrow_swappable_v<T>
If any exception is thrown, the results of the expressions bool(*this) and bool(rhs) remain unchanged.
If an exception is thrown during the call to function swap, the state of *val and *rhs.val is determined by the exception safety guarantee of swap for lvalues of T.
If an exception is thrown during the call to T's move constructor, the state of *val and *rhs.val is determined by the exception safety guarantee of T's move constructor.