Re: Extending gcjx visitor pattern

[Cédric Berger <cedric at berger dot to>]

Ranjit Mathew wrote:
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> Mike Emmel wrote:
> > I was wondering what people would think about extending the gcjx
> > visitor to also forward
> > user data.
> >
> > I.e visit_method (model_method * method,
> >                 const list<ref_variable_decl> & params,
> >                 const ref_block &block)
> >
> > would becomes
> >
> > visit_method (model_method * method,
> >                 const list<ref_variable_decl> & params,
> >                 const ref_block &block, void * visitorData );
>
> If I understand you correctly, you want the Visitor to
> say:
>
>   someObject->visit (this, opaqueBlob);
>
> and then the visited object (Visitee?) to call back
> the appropriate visit_snafu() method like:
>
>   visitorObject->visit_snafu (this, foo, bar, opaqueBlob);
>
> Right?
That's certainly the way most people implement these kind of things
int the C language, so you don't need to put your context data
(opaqueBlob) on global or thread-local memory, which is very unclean
and error-prone.

But in the OO case, you can just attach the context data inside the
visitorObject, which, if I understand correctly, is forwarded across
all the call tree. Anonymous subclasses of visitorObject might be
handy.

Cedric