metaprogramming.coffee

# I don't necessarily love CoffeeScript as a template for ES.next, but here is an example
# of metaprogramming via a combination of:
#   * "this" bound to the currently created class in class definitions
#   * class methods inherited

class Foo
  this.hasMany = (types) ->
    this.prototype[types] = ->
      alert "Looking up #{types}"

class Bar extends Foo
  this.hasMany "friends"

new Bar().friends()

metaprogramming.rb

# Similar example in Ruby

class Foo
  def self.has_many(types)
    define_method(types) { puts "Looking up #{types}" }
  end
end

class Bar < Foo
  has_many "friends"
end

Bar.new.friends