Re: [PATCH] Add internal-only port structure; move iconv descriptors there

[ludo@gnu.org (Ludovic Courtès)]

Mark H Weaver <mhw@netris.org> skribis:

> I've come to the conclusion that it is not safe to modify 'scm_t_port'
> in 2.0 at all; not even to change the member names.  In brief, the
> reason has to do with the C11 standard definition of "compatible types",
> which ties into the strict aliasing rules.  Section 6.2.7 of C11 spells
> out what it means for two structures declared in separate translation
> units to be compatible, and among other things their member names must
> be the same.

I can’t imagine how changing the *name* of a member could change
something to the structure’s layout in practice.

I would be in favor of keeping the names ‘internal’ and ‘reserved’ from
your previous patch, but if you’re really convinced that this member
name thing has a practical effect, fine with me.

> Is this a reasonable start?  Any suggestions before I proceed?

Looks good to me!

> +#define scm_gc_typed_calloc(t) ((t *) scm_gc_calloc (sizeof (t), #t))

Not really convinced by this, but hey.  Ideally, this would need to go
in the manual too.

> +typedef struct scm_t_port_internal
> +{
> +  /* input/output iconv conversion descriptors */
> +  void *input_cd;
> +  void *output_cd;
> +} scm_t_port_internal;

Please define the struct tag and typedef separately.  Also, I’d remove
‘_t’ from the struct tag, as discussed before.

Thanks for your patience & thoroughness!  :-)

Ludo’.