Is there any implementation of class interfaces for Smalltalk?

Question

In C# classes can have interfaces that can have multiple implementations. How do you do that in smalltalk?

Answer 1

First of all you typically don't need interfaces, because if an object implements the same messages as another one it can replace it. In Java and C# you cannot do this unless they are in the same hierarchy, thus you need interfaces.

• In (all) Smalltalk there are protocols (method categories) that serve the purpose of informally grouping methods together.
• In Pharo Smalltalk there are Traits. At first they look like interfaces, but they are also able to provide an implementation.

Answer 2

After a discussion today with a coworker of mine it seems to me that the answer is any class could be considered an interface because any class can be passed in a message to any other class.

Any number of classes in smalltalk can respond to the same message, therefore you don't need interfaces as per C# and java.