Retrieving the Method instance from within a metho

问题:

This is a follow-up question to How to determine the class a method was defined in? (hope you don't mind the similarity)

Given a class hierarchy, can a method retrieve its own Method instance?

class A
  def foo
    puts "A#foo: `I am #{method(__method__)}'"
  end
end

class B < A
  def foo
    puts "B#foo: `I am #{method(__method__)}'"
    super
  end
end

A.new.foo
# A#foo: `I am #<Method: A#foo>'

B.new.foo
# B#foo: `I am #<Method: B#foo>'
# A#foo: `I am #<Method: B#foo>' # <- A#foo retrieves B#foo

So that B.new.foo instead prints

# B#foo: `I am #<Method: B#foo>'
# A#foo: `I am #<Method: A#foo>' # <- this is what I want

In the previous question, Jörg W Mittag suspected that retrieving the class a method was defined in might violate object-oriented paradigms. Does this apply here, too?

Shouldn't a method "know itself"?

回答1:

I found a method that exactly does that.

class A
  def foo
    puts "A#foo: `I am #{method(__method__).super_method || method(__method__)}'"
  end
end

I really admire Matz and the Ruby core developers. The existence of such method means that they had in mind such situation, and had thought about what to do with it.

回答2:

Building on answer of How to determine the class a method was defined in? and @sawa's answer with respect to super_method, you can use:

def meth(m, clazz)
    while (m && m.owner != clazz) do 
        m = m.super_method
    end
    return m
end

class A 
  def foo
    puts "A#foo: `I am #{meth(method(__method__), Module.nesting.first)}'"
  end
end

class B < A
  def foo
    puts "B#foo: `I am #{meth(method(__method__), Module.nesting.first)}'"
    super
  end
end


B.new.foo
# B#foo: `I am #<Method: B#foo>'
# A#foo: `I am #<Method: A#foo>'

Idea here is that since we know the class/module where the method is defined by Module.nesting.first, we take the current method object found by method(__method__) and iterate through its super chain to find that instance of method whose owner is same as the class/module that defined the method.