Re: Extending GParamSpec

[Tim Janik <timj imendio com>]

On Thu, 11 Jan 2007, Laurent Marzullo wrote:

> (Sorry if this mail appear twice, but It seems that my previous post 'bounced')
>
> Hello,
>
> I?m currently writing a library and I would like to ?extend? the property and
> GParamSpec functionalities of the Glib (I?m currently writing my library in C++
> but I would like to understand some Glib stuff first).
>
> The main question I?ve Is about the best way to ?extend? GParamSpec.
>
> I would like to add (to all GParamSpec* object so, GParamSpecInt,
> GParamSpecUInt, GParamSpecInt64, etc ...) some new method and attributes.

you can derive new GParamSpecs from a GParamSpec and add fields along that way.

> 1) An attributes saying if the GValue could be null or not, and so, also
> changing the 'validate' method to check if the GValue is null or not.
> This should be for all GParamSpec*
>
> 2) I would also like to know how to retrieve the value of the 'default_value'
> parameter specified at the construction time of the GParamSpec*. I do not find
> any g_param_spec_get_default nor any field In the GParamSpecInt structure where
> this information is stored.

you can use g_param_value_set_default() to store a param spec's default in a 
GValue, or you can access the individual param specs.

> 3) I would also like to add some new attributs as length, scale, precision or a
> vector of allowed value (string value or integer, and then, checking Against
> those values when affecting a new one).

i've done that for beast, some example code implementing param specs with min/
max/stepping can be found here:
  http://svn.gnome.org/viewcvs/beast/trunk/sfi/sfiparams.h?view=markup
  http://svn.gnome.org/viewcvs/beast/trunk/sfi/sfiparams.c?view=markup
and GUI generation code based on those param specs:
  http://svn.gnome.org/viewcvs/beast/trunk/beast-gtk/gxk/gxkparam.h?view=markup
  http://svn.gnome.org/viewcvs/beast/trunk/beast-gtk/gxk/gxkparam-scale.c?view=markup

> The very first question is really how to extend the GParamSpec structure for my
> extension may also be usable to the other GParamSpecInt, GParamSpecBool, etc
> with the less code as possible.
>
> Thanks for your help
>
> +--------------------+
> + Laurent Marzullo
> +

---
ciaoTJ