From: Mike Gold <mike.gold.4433@...>
Date: 2008-10-25T20:00:55+09:00
Subject: Re: Conditionally Including Methods From A Module?

Kenny wrote:
> Is there a way to include only certain methods from a module instead
> of all the methods?

Not directly.  In general, methods are part of the same module for a 
reason.  A given method may call other methods in the module, and a 
method may use instance variables defined in other methods.

What you propose could make sense in the case of a "pure utility" module 
which has no state and where there little is or no relationship between 
the methods.

  def methods_to_lambdas(mod)
    instance = Class.new { include mod }.new
    mod.instance_methods(false).inject(Hash.new) { |hash, meth|
      hash.update(
        meth.to_sym => lambda { |*args, &block|
          instance.send(meth, *args, &block)
        }
      )
    }
  end

  def pull_methods(mod, *names)
    lambdas = methods_to_lambdas(mod)
    names.each { |name|
      define_method(name, &lambdas[name])
    }
  end

  module Misc
    def func_a ; p "Misc#func_a" ; end
    def func_b ; p "Misc#func_b" ; end
    def func_c ; p "Misc#func_c" ; end
  end

  class Fred
    pull_methods(Misc, :func_a, :func_b)
  end

  Fred.new.func_a  #=> Misc#func_a
  Fred.new.func_b  #=> Misc#func_b
  Fred.new.func_c  #=> NoMethodError

ruby-1.8.7 or 1.9 is needed for the lambda syntax (for 1.8.6 you can 
eval a string instead).
-- 
Posted via http://www.ruby-forum.com/.