From: Geert Fannes <Geert.Fannes@...>
Date: 2005-06-08T21:33:55+09:00
Subject: adding methods to classes via C

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Hello,

for performance reasons, I have to add C-implemented methods to my
classes. This works fine, but I wonder if there exist more elegant
techniques for extending inherited classes. The code hereunder indicates
what I mean. The ruby file defines the class A and method A#f (which
writes out "A#f"), and the class B, which inherits from A, but B#f is
not defined. My goal is to define B#f in a C-file. My question has to do
with how I can get the class variable cB in an elegant way.

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******the Ruby file******

#this is the base class

class A

  def f() puts('A#f') end

end

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#B inherits from A and I want to write a C-method for B#f

class B < A

  require('f.so')

end

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B.new.f

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******the C file******

#include "ruby.h"

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VALUE f0(VALUE self){printf("B#f");return self;}

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VALUE cA,cB;

void Init_f(){

//correct: results into writing out "B#f"

  cA=3Drb_define_class("A",rb_cObject);

  cB=3Drb_define_class("B",cA);

//wrong: results into writing out "A#f"

  cB=3Drb_gv_get("B");

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  rb_define_method(cB,"f",f0,0);}

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The two lines after the "correct" comment gives the correct result and
writes out "B#f", but when I use the single line after the "wrong"
comment, the method A#f is called when ruby executes B.new.f(), which
writes out "A#f". In this problem, it is still feasible to follow the
whole inheritance path to get the correct cB value since B only inherits
from A, but this becomes more of a problem when using more complex
inheritance structures. Even more, I guess it should not matter if I
modify something to the inheritance structure (unless my C-function uses
some of the inherited classes), so this is some sort of
inheritance-structure duplication that leads to maintenance problems. Is
there a more elegant method to get the class variable?

=20

Greetings,

Geert Fannes.


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