Ruby Fundamental - Alias para métodos de classe

alias_metodos_de_classe_01.rb

# You didn't write this code
class ExternalClass
  def self.class_number
    123 # Just to exemplify
  end

  def some_number
    456 # Just to exemplify
  end
end

# You wrote this code
module SomeModule
  def self.included(base)
    base.class_eval do
      alias_method :class_number_original, :class_number
      alias_method :some_number_original, :some_number

      def self.class_number
        self.class_number_original + 200
      end

      def some_number
        some_number_original + 100
      end
    end
  end
end

ExternalClass.class_number # => 123

ExternalClass.send(:include, SomeModule)
# NameError: undefined method `class_number' for class `ExternalClass'
# from (pry):16:in `alias_method'

alias_metodos_de_classe_02.rb

# You didn't write this code
class ExternalClass
  def self.class_number
    123 # Just to exemplify
  end

  def some_number
    456 # Just to exemplify
  end
end

# You wrote this code
module SomeModule
  def self.included(base)
    base.class_eval do
      alias_method :some_number_original, :some_number

      def some_number
        some_number_original + 100
      end

      class << self
        alias_method :class_number_original, :class_number

        def class_number
          class_number_original + 200
        end
      end
    end
  end
end

ExternalClass.class_number # => 123

ExternalClass.send(:include, SomeModule)
ExternalClass.class_number # => 323

alias_metodos_de_classe_03.rb

# You didn't write this code
class ExternalClass
  def self.class_number
    123 # Just to exemplify
  end

  def some_number
    456 # Just to exemplify
  end
end

# You wrote this code
module SomeModule
  def self.included(base)
    base.send(:include, InstanceMethods)
    base.extend(ClassMethods)

    base.class_eval do
      alias_method :some_number_original, :some_number
      alias_method :some_number, :some_number_new

      class << self
        alias_method :class_number_original, :class_number
        alias_method :class_number, :class_number_new
      end
    end
  end

  module InstanceMethods
    def some_number_new
      some_number_original + 100
    end
  end

  module ClassMethods
    def class_number_new
      class_number_original + 200
    end
  end
end

ExternalClass.send(:include, SomeModule)

ExternalClass.class_number          # => 323
ExternalClass.class_number_original # => 123
ExternalClass.class_number_new      # => 323

ec = ExternalClass.new
ec.some_number          # => 556
ec.some_number_original # => 456
ec.some_number_new      # => 556