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 71 .

Table 71 — optional::swap(optional&) effects [tab:optional.swap]

🔗	*this contains a value	*this does not contain a value
🔗 rhs contains a value	calls swap(val, rhs.val)	direct-non-list-initializes val with std::move(rhs.val), 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 rhs.val with std::move(val), 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 71 .

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 states of val and rhs.val are 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 states of val and rhs.val are determined by the exception safety guarantee of T's move constructor.