Re: DR#314 update

[Geoffrey Keating <geoffk at apple dot com>]

On 27/04/2007, at 2:50 AM, Joseph S. Myers wrote:

> On Fri, 26 Apr 2007, Geoffrey Keating wrote:
>
> > This seems reasonable to me, but maybe it would be simpler to write
> >
> > If there are one or more incomplete structure or union types which
> > cannot all be completed without producing undefined behaviour, the
> > behaviour is undefined.
> >
> > if that gives the same effect (which I think it does)?
>
> That suffers somewhat from the vagueness that afflicts this area (what
> rearrangements of translation units are permitted in completing the
> types?).

I wasn't thinking that the completion would necessarily be able to be  
written in the translation unit, just that there would be some  
possible completion.

>  I considered some other examples and decided that what I wanted
> was unifiability even in some cases that don't involve incomplete  
> types.
> For example:
>
> // TU 1
> void
> f (void)
> {
>  struct s { int a; };
>  extern struct s a, b;
> }
>
> void
> g (void)
> {
>  struct s { int a; };
>  extern struct s c, d;
> }
>
> // TU 2
> void
> h (void)
> {
>  struct s { int a; };
>  extern struct s a, c;
> }
>
> void
> i (void)
> {
>  struct s { int a; };
>  extern struct s b, d;
> }
>
>
> Here, each object individually has compatible types in the two  
> translation
> units - but "a" and "b" have compatible complete types within TU 1,  
> but
> incompatible complete types withing TU 2.

Hmm.  That makes sense to me, so I agree your wording is better; but  
please please make sure that this example (and the other one from the  
original DR) gets into a footnote or an example or at least the  
rationale.

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