[07/23] Add a class that multiplexes two pointer types

[Richard Sandiford]

Tom Tromey <tom@tromey.com> writes:
>>>>>> "Richard" == Richard Sandiford via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
>
> Richard> +// A class that stores a choice "A or B", where A has type T1 * and B has
> Richard> +// type T2 *.  Both T1 and T2 must have an alignment greater than 1, since
> Richard> +// the low bit is used to identify B over A.  T1 and T2 can be the same.
>
> It seems like the alignment requirement could be static_assert'd, which
> would make using this class a bit safer.

Yeah, I wondered about doing that, but in principle there's nothing
to stop people using the class for something like a char*, provided that
the start is suitably aligned.  So having gcc_checking_assert is a
compromise: it only provides run-time checking rather than compile-time
checking, but it doesn't place any artificial limits on how the class
can be used.

Thanks,
Richard