Re: [gdome]user_data and language bindings

[Claudio Sacerdoti Coen <sacerdot CS UniBO IT>]

 Hi,

> And then, obj' and newChild are just two names for the same object,
> because of some feature in ocaml?

 Not exactly. newChild is the OO wrapper, while obj' is the pre-method this.
 If you want (roughly!!) newChild is the ocaml object while obj' is the
 gdome "object".

> >     To sum up, we have two "functions" (the constructor and as_node)
> >     to map "this" of the pre-method level to objects at the OO-level.
> >     A method M at the OO level is the composition of a constructor
> >     with the pre-method M' with the as_node method.
> 
> Ok, how is this mapping performed in the constructor? Using a per-document
> this-to-OO hash table or something?

 Not at all. Simply, the constructor stores the "this" in a field of
 the object. (Roughly: in Ocaml you don't have to store fields because
 you have closures...) So, every time you call a method of the object,
 the method implementation retrieves the "this" and calls the
 pre-methods on the this and the arguments.

> First I wanted to write that I don't understand this paragraph, but having
> read it for the third time or so

 ;-))

> it becomes somewhat clear. You are in
> fact using a global or per-document hash to map the C pointers to gdome
> objects in OCaml. Well then prepare for the great programming language
> shootout :-)

 ;-)

> >  Of course, this approach is probably not feasible for other languages.
> 
> Ha! Ruby has hash tables, and so has Perl, and even C++! We could do the
> very same thing in these other languages :-) 

 Of course. My remark was just that to complete the binding I have no
 need at all for the hash table, because of the "trick" of the
 OO-objects remembering the "this" without need of any hash-table.
 So I have not really implemented the hash-table stuff, but it can be
 implemented if someone needs this (e.g. for subclassing Ocaml objects).

 I don't know if you can do the same easily in other languages
 (i.e. I don't know if you will need the hash table just to be able to
 complete the binding.)

> It's just much more efficient to simply use the user_data pointer.

 As I have said, for now it is already as efficiente as possible in the
 "standard" usage model. The hash table stuff is just for real hackers.
 And yes, I am sharing the same DOM from different languages. VERY unpolite
 of myself ;-))

> Admit: 
> I have not thought that people would want to use the same gdome tree from
> two different languages, and then still want to use the user_data
> themselves. Not really polite by these people. 

 Every time someone in my research group thinks something like that,
 I am soon going to need that. Either it is Murphy or myself ;-D

 				Happy binding,
				   C.S.C.

-- 
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Real name: Claudio Sacerdoti Coen
PhD Student in Computer Science at University of Bologna
E-mail: sacerdot cs unibo it
http://caristudenti.cs.unibo.it/~sacerdot
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