22 General utilities library [utilities]

22.6 Variants [variant]

22.6.3 Class template variant [variant.variant]

22.6.3.7 Swap [variant.swap]

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

Mandates: is_move_constructible_v<

T_{i}

> is true for all i.

Preconditions: Each

T_{i}

meets the Cpp17Swappable requirements ([swappable.requirements]).

Effects:

(3.1)
If valueless_by_exception() && rhs.valueless_by_exception() no effect.
(3.2)
Otherwise, if index() == rhs.index(), calls swap(get(*this), get(rhs)) where i is index().
(3.3)
Otherwise, exchanges values of rhs and *this.

Throws: If index() == rhs.index(), any exception thrown by swap(get(*this), get(rhs)) with i being index().

Otherwise, any exception thrown by the move constructor of

T_{i}

T_{j}

with i being index() and j being rhs.index().

Remarks: If an exception is thrown during the call to function swap(get(*this), get(rhs)), the states of the contained values of *this and of rhs are determined by the exception safety guarantee of swap for lvalues of

T_{i}

with i being index().

If an exception is thrown during the exchange of the values of *this and rhs, the states of the values of *this and of rhs are determined by the exception safety guarantee of variant's move constructor.

The exception specification is equivalent to the logical and of is_nothrow_move_constructible_v<

T_{i}

> && is_nothrow_swappable_v<

T_{i}

> for all i.