Using Metaprogramming to refactor code

If you have some methods whose definitons are similar, only different by the method name. You can use meta programming to simple the things.

Bad code:

	class User < ActiveRecord::Base
		validate_inclusion_of :activation_state, :in => ["pending", "active"]

		def self.pending_users
			find :all, :conditions => {:activation_state => 'pending'}
		end

		def self.active_users
			find :all, :conditions => {:activation_state => 'active'}
		end

		def pending?
			self.activation_state == 'pending'
		end

		def active?
			self.activation_state == 'active'
		end
	end

In this example, we have similar methods definitions of pending_users, active_users, pending, active. We can simplify the codes by using meta programming

Refactor:

	class User < ActiveRecord::Base
		STATES = ['pending', 'active']
		validate_inclusion_of :activation_state, :in => STATES

		class <<self
			STATES.each do |state|
				define_method "#{state}_users" do
					find :all, :conditions => {:activation_state => state}
				end
			end
		end

		STATES.each do |state|
			define_method "#{state}?" do
				self.activation_state == state
			end
		end
	end