Metaprogramming

In this brief piece I will examine Ruby's support for metaprogramming and how to define class level methods that add instance methods to our class implementations at run time.

Over the past few months I've been learning Ruby on Rails. One of the most attractive features of Rails its declarative style of defining relationships and validations on models; and filters on actions.

A simple example of this declarative style:

class Party < ActiveRecord::Base
  has_many :addresses
end

This class defines a Party model that can have many addresses. The simple "has_many :addresses" declaration is a great example of the power of Ruby. This simple statement adds a number of methods to our Party class, and allows us to easily manage relationships between our parties and their addresses.