Re: Caps and Options update

[Iago Toral <itoral igalia com>]

On Tue, 05 Apr 2011 10:48:32 +0200, Guillaume Emont <gemont igalia com> 
wrote:
> On 05/04/2011 09:51, Iago Toral wrote:
> > >  - for the options and caps that are defined, I think we should 
> > > have
> > > default values. I'm still hesitating on whether to put that in
> > > initialisation or in getters.
> >
> > I don't get to see the reason, in which situation do you think 
> > default
> > values for options/caps would be interesting? From what I see, when 
> > a
> > cap is not set it can only mean that the source does not support it 
> > (so
> > no need for a default value), and when a option is not set it can 
> > only
> > mean the client is not interested in that option at all (so again, 
> > no
> > need for a default value).
>
> The reason is that I need to return a value for functions like
> grl_operation_options_get_flags()/grl_caps_get_flags() (getters of
> values that are not pointers, where we cannot return NULL). 
> Otherwise,
> we would need to modify the prototype, with something like:
>
>   gboolean grl_caps_get_flags (GrlCaps *caps,
>                                GrlMetadataResolutionFlags *flags);
>
> or
>
>   GrlMetadataResolutionFlags grl_caps_get_flags (GrlCaps *caps,
>                                                  GError **error);

aha, I see now.

I think my previous point is still valid, if a particular option/cap 
does not exist it should not have any default value, that would be 
misleading I think. Probably the API should tell the client that the 
option/cap is not defined.

Now, in general I think of caps more like TRUE/FALSE properties telling 
if certain capability is supported by the source or not, in that case 
FALSE should be the default if a particular cap does not exist (== is 
not supported)

In case we do need caps with values other than a gboolean, then I'd 
have the get APIs return a gboolean as you suggest above.

BTW, do we have an example of a cap that actually needs a value that is 
not boolean? (ignoring skip, count and flags which I think should not be 
considered caps, but simply options).

In the options department though, things are different, since here is 
not about stating whether a particular feature is available or not 
(TRUE/FALSE) but to actually provide and get a specific value to be used 
for that option. In this case, just as I suggested above for the case of 
the caps with values, I would go with a gboolean result to give feedback 
on whether the option is actually present and has a proper value.

Iago