From: Brian Fundakowski Feldman <green@...>
Date: 2001-08-25T00:07:37+09:00
Subject: [ruby-talk:20291] new toy: method_var

After seeing a million examples of overriding methods in classes by aliasing 
an existing method to something with a more obscure name, defining over that 
method and then calling the alias of the old method in the new method's 
code, I convinced myself there HAD to be a better way.  In that vein, I've 
implemented the ability to "attach" an anonymous variable to a given method.

It works like this:

class Foo
    def initialize(*args)
         @bob = args
    end
    attr_reader :bob
end
class Foo
    old = instance_method(:initialize) # Hmm, I feel like overriding 
                                       # someone's Foo class and adding a
                                       # block initializer.
    def initialize(*args, &block)
         method_var.bind(self).call(*args) # Call the old constructor
         @fred = args.collect(&block) if block
    end
    define_method_var(:initialize, old) # Attach a copy of the old method to 
                                        # the current method
    attr_reader :fred
end

p Foo.new(:a, :b, :c) {|v| v.to_s}
#<Foo:0x810c508 @bob=[:a, :b, :c], @fred=["a", "b", "c"]>

Pretty simple and generalized, eh? :)  You could essentially attach any 
variable you would like to a method in this fashion, but it's most useful 
for keeping an "anonymous" copy of the old method around.  The 
implementation I came up with can be found at
<http://green.bikeshed.org/~green/ruby-mods/patch-method_var>

Let me know what you all think.

-- 
 Brian Fundakowski Feldman           \  FreeBSD: The Power to Serve!  /
 green@FreeBSD.org                    `------------------------------'