Including a Module with append_features

最新推荐文章于 2022-10-18 21:30:59 发布

最新推荐文章于 2022-10-18 21:30:59 发布 · 174 阅读

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#REST

本文探讨了在Ruby中如何利用模块的append_features方法来扩展类的功能。通过具体实例展示了如何定义类级方法和使模块的实例方法变为类方法。

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Including a Module with `append_features`

module MyMod

  def MyMod.append_features(someClass)
    def someClass.modmeth
      puts "Module (class) method"
    end
    super   # This call is necessary!
  end

  def meth1
    puts "Method 1"
  end

end


class MyClass

  include MyMod

  def MyClass.classmeth
    puts "Class method"
  end

  def meth2
    puts "Method 2"
  end

end


x = MyClass.new

                      # Output:
MyClass.classmeth     #   Class method
x.meth1               #   Method 1
MyClass.modmeth       #   Module (class) method
x.meth2               #   Method 2

This example is worth examining in detail. First, we should understand that append_features isn't just a hook that is called when an include happens; it actually does the work of the include operation. That's why the call to super is needed; without it, the rest of the module (in this case, meth1) wouldn't be included at all.

Also note that within the append_features call, there is a method definition. This looks unusual, but it works because the inner method definition is a singleton method (class-level or module-level). An attempt to define an instance method in the same way would result in a Nested method error.

Conceivably a module might want to determine the initiator of a mixin. The append_features method can also be used for this because the class is passed in as a parameter.

It is also possible to mix in the instance methods of a module as class methods.

module MyMod

  def meth3
    puts "Module instance method meth3"
    puts "can become a class method."
  end

end


class MyClass

  class << self    # Here, self is MyClass
    include MyMod
  end

end


MyClass.meth3

# Output:
#   Module instance method meth3
#   can become a class method.