CODEWITHSUNDEEP
ruby
Paritosh Singh
Paritosh Singh

Reputation: 6384

Which class in ruby is parent of all class?

I had thought that Object is an ancestor of all classes, but I tried something which made me confused.

Object.superclass # => BasicObject
Object.superclass.superclass # => nil
Object.superclass.superclass.superclass # => undefined method error since nil is not a class
Object.superclass.superclass.class # => Nilclass
Object.superclass.superclass.class.superclass # => Object

Except for nil, everything has a superclass, and nil is an instance of NilClass, so it cannot have super class method. How one can get Object as superclass of Object?

Upvotes: 0

Views: 144

Answers (3)

Arup Rakshit
Arup Rakshit

Reputation: 118271

superclassis a method of Class. Now NilClass inherits from Object. But the class Object have no chance to inherit the class Class methods.

See below from the Documentaion

Classes, modules, and objects are interrelated. In the diagram that follows, the vertical arrows represent inheritance,
and the parentheses meta-classes. All metaclasses are instances of the class `Class'.


                         +---------+             +-...
                         |         |             |
         BasicObject-----|-->(BasicObject)-------|-...
             ^           |         ^             |
             |           |         |             |
          Object---------|----->(Object)---------|-...
             ^           |         ^             |
             |           |         |             |
             +-------+   |         +--------+    |
             |       |   |         |        |    |
             |    Module-|---------|--->(Module)-|-...
             |       ^   |         |        ^    |
             |       |   |         |        |    |
             |     Class-|---------|---->(Class)-|-...
             |       ^   |         |        ^    |
             |       +---+         |        +----+
             |                     |
obj--->OtherClass---------->(OtherClass)-----------...

Yes that's correct as nil being an object of NilClass,which in turn inherits Object which is on top of the class Class. Thus Nilclass couldn't inherit superclass method.

Object.superclass.superclass #=> nil
nil.superclass #=> undefined method error since nil is not a class

Upvotes: 1

tom
tom

Reputation: 22969

From ruby-doc.org

BasicObject is the parent class of all classes in Ruby

The superclass of Object is BasicObject, and BasicObject does not have a superclass. The standard placeholder for non-existent things is nil, so BasicObject.superclass returns nil.

It so happens that nil is an instance of the class NilClass, which is a subclass of Object. This does not mean that NilClass is a superclass of BasicObject or that Object is a superclass of Object.

Upvotes: 5

Daniel Hilgarth
Daniel Hilgarth

Reputation: 174309

You don't get "Object as superclass of Object". What you get is "Object as superclass of Nilclass".

Upvotes: 4

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