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