[ruby-talk:20813] Re: Proc internals

"Christian Rishoej" <[e-mail]> wrote:
> In article <[e-mail]>, "Brian F.
> Feldman" <[e-mail]> wrote:
> 
> > They're not exactly interchangeable...  There may be an answer depending
> > on what exactly it is that you want to do.
> 
> The post from Henning von Rosen (`how update anonymous classes?'') gave
> me an excuse for investigating the internals of Ruby.
> 
> I imagined a new instance method on Class:
> 
> 	Class#add_method( methodName, &methodProc )
> 
> ....which would add the supplied Proc/Block and add it as a method to the
> particular instance of class. So far I have:
> 
> ######################################
> 
> #include "ruby.h"
> 
> VALUE
> rb_class_add_method(VALUE obj, VALUE methodName, VALUE methodProc)
> {
>     int argc;
>     ID id;
> 
>     Check_Type(methodName, T_STRING);
> 
>     if (!rb_obj_is_kind_of(methodProc, rb_cProc))
> 	rb_raise(rb_eArgError, "Must pass a Proc");
>     
>     argc = FIX2INT(rb_funcall(methodProc, rb_intern("arity"), 0));
>     
>     id = rb_intern(STR2CSTR(methodName));
>     
>    /* WHAT TO PUT HERE? */
> 
>     return Qtrue;
> }
> 
> void
> Init_add_method()
> {
>     rb_define_method(rb_cClass, "add_method", rb_class_add_method, 2);
> }
> 
> ######################################
> 
> First I thought of rb_define_method( class, name, C-function, arity ),
> but realizing that it expects a C funtion I gave up that idea.
> Then I had a look on rb_add_method which expects a NODE instead. If there
> is any way to get from a Proc to a NODE I figured I could use this.
> 
> Any comments are greatly appreciated.
> 
> Please excuse my lack of insight in the internals of Ruby.

Well, actually a proc is generally passed as a VALUE.  Check out
eval.c:rb_mod_define_method().  If you look at the code:

    if (TYPE(body) != T_DATA) {
        /* type error */
        rb_raise(rb_eTypeError, "wrong argument type (expected Proc)");
    }
    if (RDATA(body)->dmark == (RUBY_DATA_FUNC)bm_mark) {
        rb_add_method(mod, id, NEW_DMETHOD(method_unbind(body)), NOEX_PUBLIC);
    }
    else if (RDATA(body)->dmark == (RUBY_DATA_FUNC)blk_mark) {
        rb_add_method(mod, id, NEW_BMETHOD(body), NOEX_PUBLIC);
    }
    else {
        /* type error */
        rb_raise(rb_eTypeError, "wrong argument type (expected Proc)");
    }

It expects one of two things: a method itself or a block.  If you look at 
the second part, you see that it calls NEW_BMETHOD(body), which is what 
wraps the Proc to make it "become" a method.  So though they're not 
equivalent, there's a simple built-in way to make a Proc act like a real 
method at that level.

Hope this helps :)

-- 
 Brian Fundakowski Feldman           \  FreeBSD: The Power to Serve!  /
 [e-mail]                    `------------------------------'