Generated opAssign in the presence of a copy constructor

[RazvanN]

> Why the memcpy?
> This looks inefficient.
>
> Is it in case the constructor throws?
> Have a 'nothrow' case where it constructs directly to this?

The copy constructor must be called on an object in the initial 
state,
so it cannot be called directly on this as it is already 
initialized.

__dtor is used as a matter of demonstration. Indeed, xdtor is the 
the alias which points to the generated destructor (__dtor, 
__fieldDtor or __aggregatedDtor)