From: Tim Hunter <cyclists@...>
Date: 2004-07-26T03:31:54+09:00
Subject: Re: [NUBY] Iteration in extensions

Fredrik Jagenheim wrote:

> On Sun, 25 Jul 2004 13:36:54 +0900, daz <dooby@d10.karoo.co.uk> wrote:
>> 
>> You don't show how you defined 'add_values' or how you're calling it
>> from Ruby, but I think your initial array is in 'self' ...
> 
> Here is a more complete example of what I'm trying to do.
> 
>> Here's an example from enum.c (Enumerable#reject)
>> with some printf() statements added.
> 
> I'm afraid I didn't understand how to translate your example into mine.
> 
> This is basically what I'm trying to do:
> 
> -------8<------ Bitmask.c
> #include "ruby.h"
> 
> static VALUE
> bm_new(VALUE class)
> {
>   long* bitmask;
>   bitmask = ALLOC(long);
>   *bitmask = 0;
>   VALUE data = Data_Wrap_Struct(class, 0, free, bitmask);
>   return data;
> }
> 
> static VALUE
> bm_add_bit(VALUE self, VALUE bit)
> {
>   long* bitmask;
>   int int_bit = NUM2INT(bit);
>   printf("in to add_bit: %s %s\n",
>       RSTRING(rb_inspect(self))->ptr,
>       RSTRING(rb_inspect(bit))->ptr);
>   Data_Get_Struct(self, long, bitmask);
>   *bitmask |= 1 << int_bit;
>   return self;
> }
> 
> static VALUE
> bm_add_bits(VALUE self, VALUE bits)
> {
>   printf("in to add_bits: %s\n", RSTRING(rb_inspect(bits))->ptr);
>   rb_iterate(rb_each, bits, bm_add_bit, 1);
>   return self;
> }
> 
> static VALUE
> bm_value(VALUE self)
> {
>   long* bitmask;
>   Data_Get_Struct(self, long, bitmask);
>   return INT2NUM(*bitmask);
> }
> 
> VALUE cBitmask;
> 
> void Init_Bitmask() {
>   cBitmask = rb_define_class("Bitmask", rb_cObject);
>   rb_define_singleton_method(cBitmask, "new", bm_new, 0);
>   rb_define_method(cBitmask, "add_bit", bm_add_bit, 1);
>   rb_define_method(cBitmask, "add_bits", bm_add_bits, 1);
>   rb_define_method(cBitmask, "value", bm_value, 0);
> }
> 
> 
> -------8<------ test_Bitmask.rb
> 
> require 'Bitmask'
> 
> bm = Bitmask.new
> bm.add_bit(2)
> bm.add_bit(4)
> puts bm.value
> 
> bm = Bitmask.new
> bm.add_bits([2, 4])
> puts bm.value

Hmmm...the Pickaxe says this about rb_iterate:
-
VALUE rb_iterate(VALUE (*method)(), VALUE args, 
                 VALUE (*block)(), VALUE arg2);

Invokes `method' with argument `args' and block `block'. A yield from that
method will invoke `block' with the argument given to yield, and a second
argument `arg2'.

I understand that rb_iterate invokes `method' using the current self, that
is, the self that gets add_bits. Since you're passing rb_each, your class
needs to define an each method. That each method must yield and pass an
argument, which (normally) is the next member in some collection. Lastly,
the fourth arg, which becomes the 2nd argument to the block, must be a Ruby
VALUE. An integer 1 probably isn't what you want.

Overall it looks like rb_iterate isn't what you need. You want to call
add_bit for each element in the array, so I'd do something like this:

for (x = 0; x < RARRAY(bits)->len; x++)
{
   VALUE bit = rb_ary_entry(bits, x);
   (void) bm_add_bit(self, bit);
}

Or, if you want to allow for somebody subclassing your class and overriding
add_bit, replace the direct call to bm_add_bit with: 

   (void) rb_funcall(self, rb_intern("add_bit"), 1, bit);