From: Logan Capaldo <logancapaldo@...>
Date: 2006-08-29T06:01:02+09:00
Subject: Re: Partial append_features?


On Aug 28, 2006, at 3:00 PM, Ola Bini wrote:

> Hi,
>
> I'm looking for a way to copy methods from a Module, or specify  
> more directly which methods get included in a class. More or less,  
> I would like to be able to do something like this:
>
> module Foo
>   def do_one_thing
>   end
>   def do_second
>   end
>   def do_third
>   end
> end
>
> class Bar
>   append_from Foo, :do_second, :do_third
> end
>
> or
> module Baz
>   append_from Foo, :do_second, :do_third
> end
>
> and I would have a module Baz which could be included, without  
> having do_one_thing included.
>
> Is this possible in Ruby right now? My first approach was to get  
> the UnboundMethod instance_method from the Module, but I couldn't  
> find a way to attach these to an unrelated class since  
> UnboundMethod must have a is_a?-relationship with the binding object.
>
> Regards
> -- 
>  Ola Bini (http://ola-bini.blogspot.com)
>  JvYAML, RbYAML, JRuby and Jatha contributor
>  System Developer, Karolinska Institutet (http://www.ki.se)
>  OLogix Consulting (http://www.ologix.com)
>
>  "Yields falsehood when quined" yields falsehood when quined.
>
>

% cat Projects/Ruby Experiments/append_from.rb
class Module
   def append_from( mod, *methods_to_keep )
     methods_to_keep.map! { |m| m.to_s }
     methods_to_remove = mod.instance_methods(false) - methods_to_keep
     new_mod = Module.new
     new_mod.module_eval do
       include mod
       methods_to_remove.each { |meth| undef_method meth }
     end
     include new_mod
   end
end

module M
   def a
     puts "a"
   end

   def b
     puts "b"
   end
end

class A
   append_from M, :b
end

a = A.new
a.b
a.a

% ruby Projects/Ruby Experiments/append_from.rb
b
-:40: undefined method `a' for #<A:0x1e89b4> (NoMethodError)