From: Robert Klemme <bob.news@...>
Date: 2005-07-08T17:35:48+09:00
Subject: Re: Inconsistent(?) when including modules

Jason Foreman wrote:
> On 7/7/05, Paulo Jabardo <pjabardo@yahoo.com.br> wrote:
>> I was playing around with modules when I noticed that
>> I counld, for example include Math and use sin,cos,etc
>> as if it were a common method. When I tried to do the
>> same in irb
>> 
>> module Test
>>   def Test.triple(x)
>>      3*x
>>   end
>> end
>> 
>> Test.triple 2 => 6
>> 
>> If I include Test from the toplevel
>> inlcude Test
>> 
>> and then call triple directly I get an error:
>> irb(main):005:0> triple 2
>> NoMethodError: undefined method `triple' for
>> main:Object
>>         from (irb):5
>> 
>> 
>> I then tried to implement the same module as an
>> extension:
>> 
>> #include <ruby.h>
>> 
>> static VALUE triple(VALUE self, VALUE x){
>>   return rb_float_new(3.0*NUM2DBL(x));
>> }
>> 
>> VALUE modulo;
>> 
>> void Init_TestC(){
>>   modulo = rb_define_module("TestC");
>>   rb_define_module_function(modulo, "triple", triple,
>> 1);
>> }
>> 
>> When I load this extension,
>> require 'TestC.so'
>> 
>> TestC.triple 2 => 6
>> 
>> include TestC
>> triple 2 => 6   # No error
>> 
>> I haven't seen this documented. Can I get this same
>> behaviour from ruby code or do I need to write an
>> extension?
>> 
> 
> 
> You ruby module and extension module are not equivalent.  Try instead
> this: 
> 
> module Test
>   def triple(x)
>     3*x
>   end
>   module_function :triple
> end
> 
> Test.triple 2  # => 6
> 
> include Test
> triple 2       # => 6

It's even simpler:

module Test
  def triple(x)
    3*x
  end
end

>> extend Test
=> main
>> triple 2
=> 6

Kind regards

    robert