base_decorator.rb

## base_decorator.rb
class BaseDecorator
  def initialize(closure)
    @closure = closure
  end

  def bind_to(receiver)
    @closure = @closure.bind(receiver)
  end
end

## cache_decorator.rb
class CacheDecorator < BaseDecorator
  def call(*args)
    puts "Before closure"
    result = @closure.call(*args)
    puts "After closure"

    return result
  end
end

## python_like_decorators.rb
module FunctionDecorators
  def self.included(receiver)
    receiver.instance_eval {
      def decorate(decorator)
        @decorate_next_with = decorator
      end

      def method_added(name)
        if @decorate_next_with
          FunctionDecorators.apply_decorator(@decorate_next_with, name, self)
          @decorate_next_with = nil
        end
      end

      def __decorators
        @_decorators ||= {}
      end
    }
  end

  def self.apply_decorator(decorator, method_name, target)
    decorated_method = target.instance_method(method_name)

    target.send(:remove_method, method_name)

    target.__decorators[method_name] = decorator.new(decorated_method)

    new_method = <<-RUBY
      def #{method_name}(#{params = decorated_method.parameters.collect(&:last).join(',')})
        self.class.__decorators[:#{method_name}].bind_to(self)
        self.class.__decorators[:#{method_name}].call(#{params})
      end
    RUBY

    class_eval new_method
  end
end

class Object
  include FunctionDecorators
end

## usage.rb
class DBLayer
  decorate CacheDecorator
  def find(id)
    puts "Called :find with #{id}"
    puts "I am: #{self}"
  end

  def destroy; end
  def create; end

  decorate CacheDecorator
  def count
    puts "Called :count"
    return 1337
  end
end

db_layer = DBLayer.new
db_layer.find(23)
puts db_layer.count