23 General utilities library [utilities]

Requires: Lvalues of type ${\text{T}}_i$ shall be swappable ([swappable.requirements]) and is_­move_­constructible_­v<${\text{T}}_i$> shall be true for all i.

Effects:

• (2.1)

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

• (2.2)

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

• (2.3)

  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 ${\text{T}}_i$ or ${\text{T}}_j$ 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 ${\text{T}}_i$ 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 expression inside noexcept is equivalent to the logical AND of is_­nothrow_­move_­constructible_­v<${\text{T}}_i$> && is_­nothrow_­swappable_­v<${\text{T}}_i$> for all i.