Remarks: If an exception is thrown during the call to VT's constructor,
*this does not contain a value, and any previously contained value
has been destroyed.
This function shall not participate in overload resolution unless
is_copy_constructible_v<VT> is true and
is_constructible_v<VT, Args...> is true.
Remarks: If an exception is thrown during the call to VT's constructor,
*this does not contain a value, and any previously contained value
has been destroyed.
The function shall not participate in overload resolution unless
is_copy_constructible_v<VT> is true and
is_constructible_v<VT, initializer_list<U>&, Args...> is true.