Question

我正在尝试从外部添加日志记录（面向方面的风格）

class A
  def test
    puts "I'm Doing something..."
  end
end

class A # with logging!
  alias_method :test_orig, :test
  def test
    puts "Log Message!"
    test_orig
  end
end

a = A.new
a.test

上面的工作没问题，除非我再次需要为方法做别名，它会进入无限循环。我想要一些更像super的东西，我可以根据需要多次扩展它，并且每个扩展名都使用别名作为其父级。

Answer 1

另一种方法是使用未绑定的方法：

class A
  original_test = instance_method(:test)
  define_method(:test) do
    puts "Log Message!"
    original_test.bind(self).call
  end
end

class A
  original_test = instance_method(:test)
  counter = 0
  define_method(:test) do
    counter += 1
    puts "Counter = #{counter}"
    original_test.bind(self).call
  end
end

irb> A.new.test
Counter = 1
Log Message!
#=> #....
irb> A.new.test
Counter = 2
Log Message!
#=> #.....

这样做的好处是它不会使用其他方法名称污染名称空间，并且如果你想创建一个类方法add_logging或者你有什么，那么它很容易被抽象出来。

class Module
  def add_logging(*method_names)
    method_names.each do |method_name|
      original_method = instance_method(method_name)
      define_method(method_name) do |*args,&blk|
        puts "logging #{method_name}"
        original_method.bind(self).call(*args,&blk)
      end
    end
  end
end

class A
  add_logging :test
end

或者，如果你想能够在很多锅炉板上做很多方面，你可以编写一个方法来编写方面添加方法！

class Module
  def self.define_aspect(aspect_name, &definition)
    define_method(:"add_#{aspect_name}") do |*method_names|
      method_names.each do |method_name|
        original_method = instance_method(method_name)
        define_method(method_name, &(definition[method_name, original_method]))
      end
    end
  end
  # make an add_logging method
  define_aspect :logging do |method_name, original_method|
    lambda do |*args, &blk|
      puts "Logging #{method_name}"
      original_method.bind(self).call(*args, &blk)
    end
  end
  # make an add_counting method
  global_counter = 0
  define_aspect :counting do |method_name, original_method|
     local_counter = 0
     lambda do |*args, &blk|
       global_counter += 1
       local_counter += 1
       puts "Counters: global@#{global_counter}, local@#{local_counter}"
       original_method.bind(self).call(*args, &blk)
     end
  end      
end

class A
  def test 
    puts "I'm Doing something..." 
  end
  def test1 
    puts "I'm Doing something once..." 
  end
  def test2
    puts "I'm Doing something twice..." 
    puts "I'm Doing something twice..." 
  end
  def test3
    puts "I'm Doing something thrice..." 
    puts "I'm Doing something thrice..." 
    puts "I'm Doing something thrice..." 
  end
  def other_tests
    puts "I'm Doing something else..." 
  end

  add_logging :test, :test2, :test3
  add_counting :other_tests, :test1, :test3
end

Answer 2

第一选择：子类而不是覆盖：

class AWithLogging < A\
  def test
    puts "Log Message!"
    super
  end
end

第二选择：更仔细地命名你的orig方法：

class A # with logging!
  alias_method :test_without_logging, :test
  def test
    puts "Log Message!"
    test_without_logging
  end
end

然后另一个方面使用不同的原始名称：

class A # with frobnication!
  alias_method :test_without_frobnication, :test
  def test
    Frobnitz.frobnicate(self)
    test_without_frobnication
  end
end

Ruby中的跨领域日志记录

2 个答案: