A Strange Case of Inheritance Behavior

While working some code to work with the Zuora SOAP API, I got bit by a strange case of inheritance behavior. It would seem that this is related to what self is bound to during the execution of the statement. Here it is, distilled to its essentials:

class Parent def self.foo "parent foo" end def self.bar puts "parent bar" puts self.foo end end class Child < Parent def self.foo puts "child foo" end def self.bar puts "child bar" super end end puts Child.bar

Intuition will tell you that when you call Child.bar, since the method called super you would remain in the Parent context. So when the Parent.bar method called self.foo you would expect it to be kept in the same context.

This is in fact not the case; it is as if the binding of self remains with the Child class, that is why even if the self.foo was called in the Parent class the Child.foo was called instead.

I asked my colleague Aaron who was once a Python programmer to give me an equivalent Python code to run:

class Parent(object):
	def foo(self):
		print("Parent foo")
	def bar(self):
		print("Parent bar")
		return self.foo()

‚Äčclass Child(Parent):
	def foo(self):
		print("Child foo")
	def bar(self):
		print("Child bar")
		return super(Child, self).bar()

c = Child()

And the output was the same:

Child bar
Parent bar
Child foo

I’m not an expert Javascript programmer so I’m curious how an equivalent program would behave under Javascript.


Lee Siong Tai kindly provided me a fiddle here: http://www.es6fiddle.net/in0c3zsi/ and interestingly, it shows the same behavior.

Jimmy Ngu also has some interesting links, go check out our discussion at https://www.facebook.com/groups/klxrb/permalink/792231597575468/


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