Eager to please annonymous objects

6 09 2008

I’ve been doing a lot of unit testing recently, and often find myself wishing that my mock objects actually had a state. So I could push a dumb object into the system and have a look at it when it comes out, without needing to tightly couple the stubbed methods on it to the implimentation. So I’ve written up a little method that’ll help you do exactly that. It allows for javascript style annonymous objects. As soon as you try to write to an attribute or read from one the getters and setters for that attribute are created.

def annon
  # Create a new blank, basic object
  annonymous_object = Object.new

  # If a attribute is called on this object that doesn't exist
  # we want to fake it
  def annonymous_object.method_missing name, *args
    # Figure out the base name of the attribute
    method_name = name.to_s[/[^=]*/]

    # Define the getter and setter
    self.instance_eval <<-METHODS
      def #{method_name}= value
        @#{method_name} = value
      end
      def #{method_name}
        @#{method_name}
      end
    METHODS

    # Call the attribute again
    send name, *args
  end

  # Now that we've created our annonymous object
  # we'll pass it to the block. Here attributes and
  # default values to be added to the object.
  yield annonymous_object if block_given?

  # Finally return the object we've built
  annonymous_object
end
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