metaprogramming_example.rb

puts "# Test 1"
class Base1
  def self.set_message message
    @@message = message
  end
  def put_message point
    @@message % point
  end
end

class MyClass1 < Base1
  set_message "I get %d points."
end

class HisClass1 < Base1
  set_message "He gets %d points."
end
 
me = MyClass1.new
he = HisClass1.new
p me.put_message 1 #=> "He gets 1 points."
p he.put_message 2 #=> "He gets 2 points."
p me.put_message 3 #=> "He gets 3 points."

puts "\n# Test 2"
class Base2
  def self.set_message message
    class_variable_set :@@message, message
  end
  def put_message point
    self.class.class_variable_get(:@@message) % point
  end
end

class MyClass2 < Base2
  set_message "I get %d points."
end

class HisClass2 < Base2
  set_message "He gets %d points."
end

me = MyClass2.new
he = HisClass2.new
p me.put_message 1 #=> "I get 1 points."
p he.put_message 2 #=> "He gets 2 points."
p me.put_message 3 #=> "I get 3 points."

puts "\n# Test 3"
class Base3
  def self.set_message message
    define_method :put_message do |point|
      message % point
    end
  end
end

class MyClass3 < Base3
  set_message "I get %d points."
end

class HisClass3 < Base3
  set_message "He gets %d points."
end

me = MyClass3.new
he = HisClass3.new
p me.put_message 1 #=> "I get 1 points."
p he.put_message 2 #=> "He gets 2 points."
p me.put_message 3 #=> "I get 3 points."