Re: [PATCH v3 1/2] c++: Initial support for P0847R7 (Deducing This) [PR102609]

[waffl3x <waffl3x@protonmail.com>]

> (waffl3x (me))
> At a glance it seems like all I need to do then is disable the
> PTRMEM_OK_P flag then.

I'm just now realizing that I'm almost certainly wrong about this. It
still needs PTRMEM_OK_P set if there are any implicit-object member
functions in the overload set. That is, if OFFSET_REF includes that
information... but it doesn't seem like it does? Reading the
information on OFFSET_REF, particularly build_offset_ref, seems to
indicate that OFFSET_REF (at least historically) was only for things
with a pointer to member type.

> > An OFFSET_REF (with PTRMEM_OK_P) is used to express that we saw the
> > &A::f syntax, so we could build a pointer to member if it resolves to an
> > implicit-object member function.
> > 
> > For an overload set containing only a single static member function,
> > build_offset_ref doesn't bother to build an OFFSET_REF, but returns the
> > BASELINK itself.

Based on what you've said, I assume that OFFSET_REF handles static
member functions that are overloaded. But as I've said this seems to
contradict the comments I'm reading, so I'm not sure that I'm
understanding you correctly.

I suppose that will be pretty easy to test, so I'll just do that as
well.

> > I think we need the OFFSET_REF for an explicit-object member function
> > because it expresses that the code satisfies the requirement "If the
> > operand names an explicit object member function, the operand shall be a
> > qualified-id."

I do agree here, but it does reinforce that OFFSET_REF is no longer
just for members represented by pointer to member type. So that might
be something to take into consideration.

> > It might simplify things to remove the optimization in build_offset_ref
> > so we get an OFFSET_REF even for a single static member function, and
> > add support for that to cp_build_addr_expr_1.

I don't think this should be necessary, the "right thing" should just
be done for explicit-object member functions. With all the stuff going
on here that I missed I'm starting to wonder how function overloads
ever worked at all in my patch. On the other hand though, this
optimization probably could be documented better, but I very well might
have missed it even if it were.

Hell, maybe it needs a greater redesign altogether, it seems strange to
me to bundle overload information in with a construct for a specific
expression. (Assuming that's whats happening of course, I still don't
fully understand it.) It's not like this has rules unique to it for how
overload resolution is decided, right? Initializing a param/variable of
pointer to function type with an overloaded function resolves that with
similar rules, I think? Maybe it is a little different now that I write
it out loud.

I wasn't going to finish my musings about that, but it made me realize
that it might not actually be correct for address of explicit-object
member functions to be wrapped by OFFSET_REF. I mean surely it's fine
because based on what you've said static member functions are also
wrapped by OFFSET_REF, so it's likely fully implemented, especially
considering things worked before. But now that there are 2 different
varieties of class members that the address of them can be taken, it
might make sense to split things up a bit? Then again, why were static
member functions ever handled the same way? Taking the address of other
static members isn't handled in the same way here is it?

I'm probably spending too much time thinking about it when I don't
fully understand how it's all being done, I'll just go back to poking
around trying to figure it all out. Then I'll worry about whether
thing's should be done differently or not.

Alex