22 General utilities library [utilities]

22.5 Optional objects [optional]

22.5.3 Class template optional [optional.optional]

22.5.3.5 Swap [optional.swap]

constexpr void swap(optional& rhs) noexcept(see below);

Mandates: is_move_constructible_v<T> is true.

Preconditions: T meets the Cpp17Swappable requirements ([swappable.requirements]).

Effects: See Table 66 .

Table 66: optional::swap(optional&) effects [tab:optional.swap]

🔗		*this contains a value	*this does not contain a value
🔗	rhs contains a value	calls swap((this), *rhs)	direct-non-list-initializes the contained value of this with 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	direct-non-list-initializes the contained value of rhs with 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 66 .

Remarks: The exception specification is equivalent to: is_nothrow_move_constructible_v<T> && is_nothrow_swappable_v<T>

If any exception is thrown, the results of the expressions this->has_value() and rhs.has_value() 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.