Overriding instance methods of a class by mixing in a module

问题

Given a class A and a module B, mixin the instance methods of B so that it overrides the correspnding instance methods of A.

module B
  def method1
    "B\#method1"
  end

  def method2
    "B\#method2"
  end
end

class A
  def method1
    "A\#method1"
  end

  def method2
    "A\#method2"
  end

  # include B    does not override instance methods!
  #              (module gets mixed into the superclass)
end

puts A.new.method1   # want it to print out "B#method1"
puts A.new.method2   # want it to print out "B#method2"

回答1:

You could remove each of B's methods from A before including B.

class A
  def method1
    "A\#method1"
  end

  def method2
    "A\#method2"
  end

  B.instance_methods(false).each { |method|
    remove_method(method) if instance_methods(false).include?(method)
  }
  include B
end

Or from within B:

module B
  def method1
    "B\#method1"
  end

  def method2
    "B\#method2"
  end

  def self.append_features(mod)
    instance_methods(false).each { |method|
      mod.send(:remove_method, method) if mod.instance_methods(false).include?(method)
    }
    super
  end
end

回答2:

Module#include inserts the module M as a superclass of the class C. So, you can't override C's methods in M, rather it's the other way around: C's methods override M's methods. (Technically speaking, Ruby doesn't make M a superclass of C, rather it creates an invisible Include Class ⟦M′⟧ whose method table and constant table point to M's method table and constant table, and makes that class the superclass, but this distinction is not important for this particular question.)

In Ruby 2.0, there is a new method, Module#prepend which, just as the name implies, prepends M to C's ancestors, in other words, makes M a subclass of C.

So, in short: you can't, at least not yet.

来源：https://stackoverflow.com/questions/12057940/overriding-instance-methods-of-a-class-by-mixing-in-a-module

标签

ruby

module

overriding

mixins