Re: Scripting in Gnome

[James Henstridge <james daa com au>]

On 06/02/04 02:46, Bob Smith wrote:

> Exactly. This was what I was talking about when I suggested making
> GObject's self describing. a GObject could then be introspected by
> CORBA, DBus, Python, Whatever to allow the scripting functionality
> easily. I think GObject's properties are self describing currently but
> methods are not. Anyone know what else would need to be described to
> make this possible?
>  
The ORBit2 IInterface IDL would be worth looking at for this kind of 
thing.  You basically want:

   * get the type of an object (we already have this with
     G_OBJECT_GET_CLASS() or G_OBJECT_TYPE()).
   * A way to find all base classes of a particular class (also already
     available).
   * A way to get a list of the methods of a class.
   * For each method on the class:
         o The return type
         o List of argument names (you might consider this optional)
         o List of argument types
         o Whether each argument is in, out or inout.
   * Require that all function arguments and return values can be
     represented by the type system (this requires a fair bit of
     work).  This might involve extending the type system.
   * Some way to invoke a method on an instance programatically.


The last one is probably most difficult.  The two ways to solve it are 
to generate marshalling code (similar to what we do for signals), or use 
something like libffi to construct the function calls (probably making 
use of the interface information to help construct the call).

For GTK, we haven't really had to worry about this because C can already 
call C functions quite easily :)  For CORBA, they needed to deal with 
this from the start, since they needed to be able to convert invocations 
from the network into function calls.

Note that most of the language bindings for dynamic languages actually 
implement most of this already.  Unfortunately, the format they expose 
all the class information in is "Python classes" or "Perl classes", and 
method calls are done using the "Python method call interface" or "Perl 
method call interface" :)  This isn't very helpful if you are trying to 
use the information from a language other than the one the binding is 
for ...

James.

--
Email: james daa com au
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