Question

This article speaks of the difference between types and classes. Since I ve only worked with languages that treat both as identical, please suggest material/programming-languages that will teach me the difference.

Answer 1

Difference is not the right word - classes are certainly types. But not all types are classes. Note also that the word "class" is quite vague - it could be just a tuple type (with no operations except construction and projection - a C struct so to speak) or, on the other side of the spectrum, a class that contains only methods, but no state.

Answer 2

Sather is the oldest language i know of which treats types and classes separately. However, it is not completely rigorous, as one can still use a class as a variable type (i think), one just can t subtype it.

This is not terribly different from what C++ lets you do: you can use purely abstract classes to define types, and have all concrete classes implement them using public inheritance, but subclass each other using private inheritance. You then use the abstract classes for variable types, using the concrete classes only in constructor expressions.

Java lets you do more or less the same, defining types using interfaces and implementations using classes, but because there is no private inheritance, there is no way to hide the inheritance relationship of the classes.

Does that make any sense at all?

Answer 3

Java, pre-autoboxing. int and Integer are both types, but only the latter is a class.

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