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GNU Smalltalk User's Guide

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4.4.1 Creating a new class

Guess how you create a new class? This should be getting monotonous by now--by sending a message to an object. The way we create our first "custom" class is by sending the following message:

 
   Object subclass: #Account
       instanceVariableNames: 'balance'
       classVariableNames: ''
       poolDictionaries: ''
       category: nil !

Quite a mouthful, isn't it? Most people end up customizing their editor to pop this up at a push of a button. But conceptually, it isn't really that bad. The Smalltalk variable Object is bound to the grand-daddy of all classes on the system. What we're doing here is telling the Object class that we want to add to it a subclass known as Account. The other parts of the message can be ignored, but instanceVariableNames: 'balance' tells it that each object in this subclass will have a hidden variable named balance. (23)


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