Re: Scripting in Gnome

[James Henstridge <james daa com au>]

On 06/02/04 11:33, Bob Smith wrote:

> Hmm... This would be a lot of work to program in all this information
>
> manually. 
>
> I believe the GTK# project has a program that analyzes C files and
> produces an XML description of the GObjects... If they do, maybe it
> could be modified or an XSLT document be created to convert that
> information to a form that can be automatically linked into a
> library/program.
>  
The interface descriptions in GTK# (which are actually quite similar to 
the s-expression based ones most other language bindings use) are not 
quite what I was referring to, since it doesn't really tie into a type 
system very well.  If you look at the ORBit2 code, you get a 
CORBA::TypeCode for each function argument and one for the return value.

Each typecode has a kind (which is picked from a fixed size enum), such 
as "int", "enum", "string", "struct", "sequence" or "interface".  For 
the struct type, you can get a list of the struct member names along 
with TypeCodes describing the types of the members.  This makes it quite 
easy to write a finite amount of code that can convert pretty much any 
CORBA type into a Python equivalent, for instance.

The other reason for not picking XML is that it isn't very shareable, so 
each application that loads the interface description will have a 
separate copy in memory.  In contrast, ORBit IInterfaces are usually 
static data loaded from a shared library, so are quite shareable.  
Similarly Mozilla's XPCOM type libraries are structured in such a way 
that they can be mmaped read only, making it shareable between multiple 
processes.

> >    * 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).
> >    
>
> Yeah. Mono seems to be doing fairly well doing this sort of thing. Maybe
> their team can provide a good solution to the problem.
>  
Yep.  It looks like they are using libffi.  If the scripting framework 
ended up using libffi, I would hope that it has some layer on top that 
is a bit easier to use ...

> Know how COM on Python works? Does it create proxy Python objects? We
> could do the same thing...
>  
Invocations are performed using the IDispatch interface, IIRC.  It can 
run in two modes -- in one it generates Python source files that call 
Dispatch from a COM typelib.  In the other it does everything at runtime.

James.

--
Email: james daa com au
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