What is a built-in class?

A built-in class is a class whose instances have restricted capabilities or special representations . Attempting to use defclass to define subclasses of a built-in class signals an error of type error. Calling make-instance to create an instance of a built-in class signals an error of type error.

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When should I define a class?

As a rule of thumb, when you have a set of data with a specific structure and you want to perform specific methods on it , use a class. That is only valid, however, if you use multiple data structures in your code. If your whole code won’t ever deal with more than one structure.

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