Question

I have two C extensions for Ruby (for a Rails app). I initialize these in application.rb with config.after_initialize.

Here is the first Class:

class Object
  require 'inline'

  inline do |builder|

    builder.c <<-EOC
      static VALUE 
      rb_obj_is_number(){
        // code to return Qtrue or Qfalse
      }
    EOC

  end

  alias is_number rb_obj_is_number

end

Here is the second (which needs to use rb_obj_is_number() from above):

class Array
  require 'inline'

  inline do |builder|

    builder.c <<-EOC
      static VALUE 
      rb_ary_some_fun(){
        double result = 0;
        long i, len = RARRAY_LEN(self);
        VALUE *c_arr = RARRAY_PTR(self);

        for(i=0; i<len; i++) {
          if ( TYPE(rb_obj_is_number(c_arr[i])) == T_TRUE ) {       
            result += NUM2DBL(c_arr[i]);
          }
        }
        return rb_float_new(result);
      }
    EOC
  end

  alias some_fun rb_ary_some_fun

end

While trying to call a function from one file to another I get the following error:

dyld: lazy symbol binding failed: Symbol not found: _rb_obj_is_number

I guess this is because I did not include the first generated file in the second.
How can I do that in order to have rb_obj_is_number recognized by the compiler?

Answer 1

Your functions are declared as static in separate compilation units so of course rb_ary_some_fun cannot see rb_obj_is_number. Two options immediately come to mind:

One options is to put the C implementation of rb_obj_is_number in a String that is accessible to both builder.c calls. This will give you two copies of the function but:

• Both implementations will be static so you won’t have namespace issues.
• The implementation is probably small enough that the extra bloat won’t be a problem.
• Both implementations will come from the same String so you shouldn’t have a problem keeping them the same.

You’d have something like this:

# In some library file...
module CUtil
  IS_NUMBER = %q{
    static VALUE rb_obj_is_number(void) { /*...*/ }
  }
end

# When monkey patching Object...
class Object
  require 'inline'
  inline do |builder|
    builder.c CUtil::IS_NUMBER
  end
  alias is_number rb_obj_is_number
end

# When monkey patching Array...
class Array
  require 'inline'
  inline do |builder|
    builder.c <<-EOC
      #{CUtil::IS_NUMBER}
      static VALUE rb_ary_some_fun(void) { /*...*/ }
    EOC
  end
  alias some_fun rb_ary_some_fun
end

That’s a big pile of kludge so I wouldn’t recommend it. There are probably cases where that approach makes sense though.

The right way to do this is to call is_number as a Ruby method from your C. Calling is_number as a method allows it to be overridden, monkey patched, etc. just like any other method. You’d use rb_funcall something like this:

/* There's no need to call this over and over again inside a loop. */
ID is_number = rb_intern("is_number");
/* ... */
if(rb_funcall(c_arr[i], is_number, 0) == Qtrue) {
    result += NUM2DBL(c_arr[i]);
}

Also, I recommend that you use proper function signatures (i.e. rb_obj_is_number(void)) to make sure your compiler doesn’t end up in K&R mode. You should also adjust your compiler’s warning flags so that it complains loudly about that sort of thing.