Ruby 中的横切日志 [英] Cross-cutting logging in Ruby

问题描述

我正在尝试从外部向方法添加日志记录(面向方面​​的风格)

I'm trying to add logging to a method from the outside (Aspect-oriented-style)

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

以上工作正常，除了如果我需要再次为方法做别名，它会进入无限循环.我想要更像 super 的东西，在那里我可以根据需要扩展它多次，并且每个扩展名都有其父级的别名.

The above works alright, except that if I ever needed to do alias the method again, it goes into an infinite loop. I want something more like super, where I could extend it as many times as I needed, and each extension with alias its parent.

推荐答案

另一种选择是使用未绑定的方法:

Another alternative is to use unbound methods:

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用额外的方法名称污染命名空间，而且很容易抽象，如果你想创建一个类方法 add_logging 或者你有什么.

This has the advantage that it doesn't pollute the namespace with additional method names, and is fairly easily abstracted, if you want to make a class method add_logging or what have you.

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，如果您希望能够在没有大量样板的情况下完成一系列方面，您可以编写一个方法来编写方面添加方法！

Or, if you wanted to be able to do a bunch of aspects w/o a lot of boiler plate, you could write a method that writes aspect-adding methods!

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

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