rubylearning.org - metaprogramming - method wrapper

aliasing.rb

module RubyLearning
  module Module

    WRAPPER_PREFIX = 'wrapper_'
    WRAPPED_PREFIX = 'wrapped_'


    def before(method, prev_option = {})
      prev_option.merge!(:before => normalize_method_name(method))
    end

    def after(method, prev_option = {})
      prev_option.merge!(:after => normalize_method_name(method))
    end

    def wrap(original_method, &block)
      define_wrapper(yield, original_method)
      alias_method_chain(original_method, "#{WRAPPER_PREFIX}#{original_method}")
    end

    private
    def normalize_method_name(method)
      class_eval do
        if method.respond_to? :call
            method_name = "#{WRAPPER_PREFIX}#{method}"
            define_method(method_name , &method)
            method_name
          else
            method
          end
      end
    end
    
    def alias_method_chain(target, feature)
      class_eval do
        alias_method "#{WRAPPED_PREFIX}#{target}", target
        alias_method target, feature
      end
    end

    def define_wrapper(wrappers, original_method)
      class_eval do
        define_method "#{WRAPPER_PREFIX}#{original_method}" do
          send(wrappers[:before]) if wrappers[:before]
          send("#{WRAPPED_PREFIX}#{original_method}")
          send(wrappers[:after]) if wrappers[:after]
        end
      end
    end

  end
end

rubyist.rb

# rubyist.rb
class Rubyist
  def initialize name
    @name = name
    @count = 0
  end

  def say!
    puts 'hello'
  end
end

rubyist_with_count.rb

# rubyist_with_count.rb

require 'rubyist'
require 'aliasing'

class Rubyist
  extend RubyLearning::Module

  def in_method
    @count += 1 
    p "#{@name}(#{@count}) starts greeting ..."
  end

  wrap :say! do
    #before :in_method, after(lambda { p "#{@name}(#{@count}) finished greeting ..." })
    #before :in_method
    #after lambda { p "#{@name}(#{@count}) finished greeting ..." }
    after :in_method, before(lambda { p "#{@name}(#{@count}) finished greeting ..." })
  end
end

simple1.rb

# simple1.rb

class MyClass
  def greet
    puts "Hello lo yaaah!"
  end
end

MyClass.new.greet  # => Hello!

simple2.rb

# simple2.rb

require 'simple1'

class MyClass
  def greet_with_log
    puts "Calling method..."
    puts "Hello!"
    puts "...Method called"
  end

  alias_method :greet, :greet_with_log
end

MyClass.new.greet

# => Hello!
#    Calling method...
#    Hello!
#    ...Method called

test_snippet.rb

# test_snippet.rb

require 'rubyist'
satish = Rubyist.new('Satish')
3.times{satish.say!}

puts '-' * 20

require 'rubyist_with_count'
3.times{satish.say!}