Question

Interface (or an abstract class with all the methods abstract) is a powerful weapon in a static-typed language such as C#, JAVA. It allows different derived types to be used in a uniformed way. Design patterns encourage us to use interface as much as possible.

However, in a dynamic-typed language, all objects are not checked for their type at compile time. They don’t have to implement an interface to be used in a specific way. You just need to make sure that they have some methods (attributes) defined. This makes interface not necessary, or at least not as useful as it is in a static language.

Does a typical dynamic language (e.g. ruby) have interface? If it does, then what are the benefits of having it? If it doesn’t, then are we losing many of the beautiful design patterns that require an interface?

Thanks.

Answer 1

I guess there is no single answer for all dynamic languages. In Python, for instance, there are no interfaces, but there is multiple inheritance. Using interface-like classes is still useful:

• Interface-like classes can provide default implementation of methods;
• Duck-typing is good, but to an extent; sometimes it is useful to be able to write isinstance(x, SomeType), especially when SomeType contains many methods.