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 [tab:optional.swap].
| *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 [tab:optional.swap].
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.