Dynamically Add Methods to Classes Through their Objects in Ruby

Playing with the implementation of a new library I am working on called starfish (I will blog about it shortly), I came up with this fun little Ruby hack that makes Ruby seem more like a prototype-based language than it already does.

class Foo
  def method_missing(name, *args)
    if name.to_s =~ /(.*)=$/ && args[0].is_a?(Proc)
      self.class.instance_eval do
        define_method($1, args[0])
      end
    else
      super
    end
  end
end

f = Foo.new
f.greet = lambda {|t| "Hello #{t}!"}
f.greet "Lucas Carlson" # => Hello Lucas Carlson!

j = Foo.new
j.greet "World" # => Hello World!

Hope you enjoy it as much as I do and I can't wait to show you how I am using it!

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