From: Robert Dober <robert.dober@...>
Date: 2008-01-19T20:51:26+09:00
Subject: Re: passing method references in python & ruby

On Jan 18, 2008 6:50 PM, rpardee@gmail.com <rpardee@gmail.com> wrote:

> My momentary python envy (hmmm...) has now passed. ;-)
Well that is good, but for the wrong reason :(

Our Rubyists where cheating on you as you had a first class object
called a function, and we were just using names.
Now there are no functions in Ruby so we cannot pass them on, we do
however have proc objects which would mimick what you have done in
Python
firstway =lambda{ |x| x+1}
otherway = lambda{ |x| x - 1}
def anyway away, anumber
    away.call anumber
end

However the interesting and somewhat frustrating stuff starts with
methods which are first class objects in Ruby
class A
    def first x; x+1 end
    def second x; x-1 end
    @f = instance_method :first
    @s = instance_method :second
    class << self
       attr_reader :f, :s
    end

    def any method, number
        method.bind( self ).call number
    end
end

p A.new.any(A.f, 41)
p A.new.any(A.s,43)

Things are however a little bit trickier when it comes to binding
instance_methods
look at this code
class B
   def b; 42 end
end

p B.instance_method(:b).bind(Object.new).call # :(((
I still fail to see the need for this restriction
Now lots of trickery is needed if you want to do things like these

module M
  def m; 42 end
end

p Object.new.send(:extend, M).m

If you are interested in this stuff you might have a look at the
implementation of Traits in Ruby
http://rubyforge.org/projects/ruby-traits/
HTH
Robert

-- 
http://ruby-smalltalk.blogspot.com/

---
Whereof one cannot speak, thereof one must be silent.
Ludwig Wittgenstein