23 General utilities library [utilities]

23.7 Variants [variant]

23.7.3 Class template variant [variant.variant]

23.7.3.6 Swap [variant.swap]

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

Requires: Lvalues of type shall be swappable ([swappable.requirements]) and is_­move_­constructible_­v<> shall be true for all i.

Effects:

  • if valueless_­by_­exception() && rhs.valueless_­by_­exception() no effect. Otherwise,

  • if index() == rhs.index(), calls swap(get<i>(*this), get<i>(rhs)) where i is index(). Otherwise,

  • exchanges values of rhs and *this.

Throws: If index() == rhs.index(), any exception thrown by swap(get<i>(*this), get<i>(rhs)) with i being index(). Otherwise, any exception thrown by the move constructor of or with i being index() and j being rhs.index().

Remarks: If an exception is thrown during the call to function swap(get<i>(*this), get<i>(rhs)), the states of the contained values of *this and of rhs are determined by the exception safety guarantee of swap for lvalues of 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 expression inside noexcept is equivalent to the logical AND of is_­nothrow_­move_­constructible_­v<> && is_­nothrow_­swappable_­v<> for all i.