floppy.rb

class Floppy

  def metaclass
    class << self
      return self
    end
  end

  def metaclass_eval(&block)
    metaclass.class_eval(&block)
  end

  def method_missing(method_name, *args)
    super unless method_name.to_s.end_with?("=") && args.length == 1 

    proc = args.first
    reader_name = method_name.to_s[0..-2] # :abc= => "abc"

    unless proc.is_a?(Proc)        # for define method we must use a proc
      proc = lambda { args.first } # if we said "lambda { proc }" we'd just get our lambda back
    end

    metaclass_eval do
      define_method(reader_name, proc)  
    end  
  end  
end

require 'test/unit'

class FloppyTest < Test::Unit::TestCase
  
  def setup
    @foo = Floppy.new
  end
  
  def test_assign_proc_adds_method
    @foo.bar = lambda { "bar" }
    assert_equal "bar", @foo.bar
  end
  
  def test_assign_object_add_attr
    @foo.name = "Foo"
    assert_equal "Foo", @foo.name
  end

  def test_assign_object_then_attr
    @foo.name = "Foo"
    assert_equal "Foo", @foo.name

    @foo.name = lambda {|n| "Foo #{n}"}
    assert_equal "Foo 4", @foo.name(4)

    @foo.name = "Fooble"
    assert_equal "Fooble", @foo.name
  end
  
  def test_method_method_still_works
    assert_raise NoMethodError do
      @foo.alakazam
    end
  end
  
end