如何拦截ruby中的方法调用? [英] How can I intercept method call in ruby?

问题描述

我目前有一个超类，它有一个函数，我希望所有子类在它的每个函数中调用它.该函数的行为应该类似于 rails 中的 before_filter 函数，但我不确定如何实现 before_filter.这是一个例子

I currently have a superclass which has a function that I want all the subclass to call within each of its function. The function is supposed to behave like a before_filter function in rails but I am not sure on how to go about implementing before_filter. Here is an example

class Superclass
  def before_each_method
    puts "Before Method" #this is supposed to be invoked by each extending class' method
  end
end

class Subclass < Superclass
  def my_method
    #when this method is called, before_each_method method is supposed to get invoked
  end
end

推荐答案

这是一种方法:

class Superclass
  def before_each_method name
    p [:before_method, name]
  end

  def self.method_added name
    return if @__last_methods_added && @__last_methods_added.include?(name)
    with = :"#{name}_with_before_each_method"
    without = :"#{name}_without_before_each_method"
    @__last_methods_added = [name, with, without]
    define_method with do |*args, &block|
      before_each_method name
      send without, *args, &block
    end
    alias_method without, name
    alias_method name, with
    @__last_methods_added = nil
  end
end

class SubclassA < Superclass
  def my_new_method
    p :my_new_method
  end

  def my_new_other_method
    p :my_new_other_method
  end
end

SubclassA.new.my_new_method
SubclassA.new.my_new_other_method

这将使用 alias_method_chaining 方法创建一个包装方法，只要您要包装的方法在子类中定义.

This will create a wrapper method using the alias_method_chaining method as soon as the method you'd like to wrap is defined in the subclass.

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