Hands-On Design Patterns and Best Practices with Julia

The square-rectangle problem

Julia does not support implementation inheritance. Let's list the reasons:

• All concrete types are final, so there is no way to create new subtypes from another concrete type. Therefore, it is not possible to inherit object fields from anywhere.
• You cannot declare any field in an abstract type because otherwise, it would be concrete rather than abstract.

The core developers of the Julia programming language made a very early design decision to avoid implementation inheritance for a number of reasons. One of them is the so-called square-rectangle problem, also sometimes called the circle-ellipse problem.

The square-rectangle problem presents a clear challenge for implementation inheritance. As we know by common ...