20 General utilities library [utilities]

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