From: Trans <transfire@...>
Date: 2006-03-19T23:13:49+09:00
Subject: Re: Functor Opinion

> Can you elaborate a bit more the benefits and use cases of this class?
> Thanks!

Sure.

I'm aware that technically a Functor is nothing more than a first class
function. But Ruby already has a class for this, Proc (not to mention
Method). The class I present could more precisely be labeld a
"MetaFunctor". But since there's nothing of use to define as Functor in
Ruby I just dropped the "Meta" prefix. I'm all ears, if anyone has a
truly better name.

One could define #call and #[] for this class too, but we don't really
want to, because we want to keep as many methods available for passing
thru to method_missing as possibe. (Hence the subclass of BasicObject,
ie. BlankSlate).

I generally use it to create a separate method space for a class.
Here's an example of one place I've used it:

# facet/kernel/__meta__.rb

 begin
   require 'calibre/functor'
 rescue LoadError
   require 'facet/functor'
 end

 class Object

  # Returns a Functor that allows one to call any
  # Kernel method bound to self.
  #
  #   class A
  #     def object_id ; "OBTUSE" ; end
  #   end
  #
  #   c = C.new
  #   c.object_id             #=> "OBTUSE"
  #   c.__meta__.object_id    #=> 6664875832
  #
  def __meta__
    @__meta__ ||= Functor.new do |meth, *args|  # &blk|
      Kernel.instance_method(meth).bind(self).call(*args) # ,&blk)
    end
  end

 end

Additionally, the Functor can also be used as a quick and simple
delegator or proxy.

T.