Re: [AD] file interface fopen

[Peter Wang <novalazy@xxxxxxxxxx>]

On 2010-12-19, Matthew Leverton <meffer@xxxxxxxxxx> wrote:
> On Sun, Dec 19, 2010 at 5:09 PM, Peter Wang <novalazy@xxxxxxxxxx> wrote:
> > On 2010-12-19, Matthew Leverton <meffer@xxxxxxxxxx> wrote:
> >> If the current interfaces (stdio, etc) used the userdata pointer
> >> instead of the struct extension, then there would only need to be a
> >> single fi_open hook.
> >
> > You could make all the fi_* methods take the userdata pointer in
> > addition to or instead of the ALLEGRO_FILE argument.
> >
> I didn't change anything in stdio (etc) just because I didn't want to
> make a lot of changes if the general idea wasn't received.
> 
> If we make the assumption that all custom file interfaces will contain
> user extended data, then it could return that instead:
> 
> void *fi_open(const char *filename, const char *mode) { }
> 
> Returning NULL would mean that the file could not be opened.
> Otherwise, the returned pointer is set to the ->userdata. Thus this
> eliminates the need for access to the internals, and it removes the
> need for a userdata setter.

Sounds okay.

> 
> And, as you've mentioned, if the user data is passed to all other
> functions, you wouldn't need a getter either. [But it would still be
> useful for interface-specific methods, like
> al_memfile_resize(ALLEGRO_FILE *) or something.]
> 
> Also, there's:
> 
> ALLEGRO_FILE *al_create_file_handle(ALLEGRO_FILE_INTERFACE *vt,  void
> *userdata);
> 
> That would just skip the fi_open vt call. It's primary purpose would
> be for use by interfaces like memfile. Or is it better for
> consistency's sake to have:
> 
> al_fopen(const char *path, const char *mode);
> al_fopen_vt(ALLEGRO_FILE_INTERFACE *vt, const char *path, const char *mode);
> al_create_file_handle(void *userdata);
> al_create_file_handle_vt(ALLEGRO_FILE_INTERFACE *vt,  void *userdata);
> 
> where the vt versions bypass the default interface?

al_fopen_vt perhaps has a purpose.  I can't see one for
`al_create_file_handle(void *userdata)'.  A concern is that you might
accidentally pair the default interface with an unrelated userdata.

> You also had mentioned "void al_destroy_file_handle(ALLEGRO_FILE
> *f);", but I don't see how that differs from al_fclose();

No, I didn't think it through.

Peter