Inheritance and Lookup

5: Lookup in metaclasses

Goal

1. in Pharo, everything is an object
2. objects can receive messages
3. classes are objects too

Classes can receive messages. The mechanism is exactly the same

Only One Lookup Rule

The lookup starts in the class of the receiver then:

• if the method is defined in the class, it is returned
• otherwise the search continues in the superclass

A Class is an Instance of Another Class

Class X is always the unique instance of the class X class:

• Node is a class and an object
• each object is an instance of a class
• the class of Node is Node class
• the class Node class is automatically created

Superclass Chain

Lookup of Class Methods is No Different

What You Should Know

• A class is an object
• A class can receive messages
• Method lookup is exactly the same as for all objects:
  • go to the class of the receiver
  • follow inheritance chain
• More during the lecture Understanding Metaclasses