Some meta-progging example in Ruby

person.rb

class Person
  
  @people = []
  @@id = 0
  
  attr_accessor :id, :name, :age
  
  def initialize(args)
    @id = (@@id += 1)
    @name = args[:name]
    @age  = args[:age]
  end
  
  def to_params
    "?name=#{name}&age=#{age}"
  end
  
  class << self
    
    def create(args)
      @people << Person.new(args)
      @people.last
    end 
    
    def find(id) 
      @people.find{|person| person.id == id}
    end
    
    def find_by(attribute,value)
      @people.select{|person| person.instance_variable_get("@#{attribute}") == value }
    end
    
    def method_missing(method_name,*args,&block)
      if method_name.to_s.match(/find_by_(\w+)/)
        method_name.to_s.match(/find_by_(\w+)/)
        attribute = Regexp.last_match(1)
        find_by(attribute,args.shift)
      else
        super
      end
    end
    
  end
end

Person.create(:name => "Thomas", :age => 38)
Person.create(:name => "Espen", :age => 19)
p Person.find_by_name("Espen")