From: dblack@...
Date: 2007-05-05T06:47:58+09:00
Subject: Re: modules and class methods.

Hi --

On Fri, 4 May 2007, Brad Phelan wrote:

> Brad Phelan wrote:
>> Why does this not work!
>> 
>> ########################################
>> module Foo
>>     def self.foo a
>>     puts a
>>     end
>> end
>> 
>> class Bar
>>    include Foo
>>    foo "hello"
>> end
>> 
>> foo.rb:20: undefined method `foo' for Bar:Class (NoMethodError)
>> ####################################
>> 
>> but this does
>> 
>> class Bar
>>    def self.foo a
>>     puts a
>>     end
>>    foo "hello"
>> end
>> 
>> 
>> 
>> What am I misunderstanding about modules????
>> 
>> -- 
>> Brad
>> http://xtargets.com
>
> The below code obviously work the way I wish
>
> module Foo
>   def foo
>      puts "a"
>   end
> end
>
> class Bar
>   extend Foo
>   puts foo
> end
>
> however is there any way to get the same effect by using include. I would 
> like to mix in class and instance methods in one call. It seems
> I can do one or the other but not both at the same time. Is that
> correct?

Basically, yes: mixing in a module inserts the module in only one
method lookup path, and a class and its instances generally have very
different lookup paths.

You can use the inherited hook in Module to do both -- for example:

   module M
     def self.included(c)
       m = self
       c.class_eval { extend m }
     end

     def meth
       puts "here"
     end
   end

   class C
     include M
   end

   C.meth          # here
   C.new.meth      # here


David

-- 
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