Question

我希望能够来回切换实例如何响应消息。我希望通过混合模块，然后在另一个模块中混合来覆盖该行为来做到这一点。

示例：

module Dog
  def speak
    puts "woof woof"
  end
end

module Cat
  def speak
    puts "meow"
  end
end

class Animal
end

现在我想来回切换Animal的实例如何响应speak消息：

animal = Animal.new

animal.extend(Cat)
animal.speak

animal.extend(Dog)
animal.speak

animal.extend(Cat)
animal.speak

animal.extend(Dog)
animal.speak

animal.extend(Cat)
animal.speak

我希望此代码输出以下内容：

meow
woof woof
meow
woof woof
meow

相反，它输出如下：

meow
woof woof
woof woof
woof woof
woof woof

有关如何使其按预期工作的任何提示？

Answer 1

我在Adapter Pattern in ruby: Accessing Your Instance Variables

的另一个问题上调整了答案

module Dog
  def speak
    puts "woof woof"
  end
end

module Cat
  def speak
    puts "meow"
  end
end

module Module_manager
  attr_accessor :name
  def extend mod
    @ancestors ||= {}
    return if @ancestors[mod]
    remove @name if @name
    @name = mod
    mod_clone = mod.clone
    @ancestors[mod] = mod_clone
    super mod_clone
  end

  def remove mod
    mod_clone = @ancestors[mod]
    mod_clone.instance_methods.each {|m| mod_clone.module_eval {remove_method m } }
    @ancestors[mod] = nil
  end
end

class Animal
  include Module_manager
end

animal = Animal.new

animal.extend(Cat)
animal.speak # meow

animal.extend(Dog)
animal.speak # woof woof

animal.extend(Cat)
animal.speak # meow

animal.extend(Dog)
animal.speak # woof woof

animal.extend(Cat)
animal.speak # meow

Answer 2

我不确定以下内容是否能回答您的问题，但这是实现相同行为的更简单方法。

class Animal
  include Dog
  alias :dog_speak :speak
  include Cat
  alias :cat_speak :speak
  private :dog_speak, :cat_speak

  def initialize
    @speak_to_me = [:cat_speak, :dog_speak].cycle
  end  

  def speak
    send @speak_to_me.next
  end
end

animal = Animal.new
  #=> #<Animal:0x007fe3a222b0e0 @speak_to_me=#<Enumerator:
  #     [:cat_speak, :dog_speak]:cycle>> 

animal.speak #-> meow
animal.speak #-> woof woof
animal.speak #-> meow
animal.speak #-> woof woof

通过在另一个模块中混合来覆盖模块混合行为

2 个答案: