Multiple Inheritance in Ruby?

Question

I thought that Ruby only allowed single inheritance besides mixin. However, when I have class Square that inherits class Thing, Thing in t

Answer 1

Multiple inheritance - This is absolutely not possible in ruby not even with modules.

multilevel inheritance - This is what is possible even with the modules.

Why ?

Modules acts as an absolute superclasses to the class that includes them.

Ex1 :

class A
end
class B < A
end

This is a normal inheritance chain, and you can check this by ancestors.

B.ancestors => B -> A -> Object -> ..

Inheritance with Modules -

Ex2 :

module B
end
class A
  include B
end

inheritance chain for above example -

B.ancestors => B -> A -> Object -> ..

Which is exactly same as a Ex1. That means all the methods in module B can override the methods in A, And it acts as a real class inheritance.

Ex3 :

module B
  def name
     p "this is B"
  end
end
module C
  def name
     p "this is C"
  end
end
class A
  include B
  include C
end

A.ancestors => A -> C -> B -> Object -> ..

if you see the last example even though two different modules are included they are in a single inheritance chain where B is a superclass of C, C is a superclass of A.

so,

A.new.name => "this is C"

if you remove the name method from module C, above code will return "this is B". which is same as inheriting a class.

so,

At any point there is only one multilevel inheritance chain in ruby, which nullifies having multiple direct parent to the class.