A lot of people are on the “composition over inheritance” bandwagon now, but I’ve honestly not seen a situation where I felt that inheritance was used and was the wrong choice. (Though most of my experience is in python where there’s no diamond problem, mixin classes are common, etc)
What I noticed is that everyone seems to agree that inheriting implementation is useful, because you have that with traits in rust (which are agreed to be good, afaik), so in languages without traits, it seems reasonable to want to use the next best thing
Mixins are composition! They don’t describe what a type is (“circle” is a “shape”, etc) but rather what they can do (“circle” can have its area calculated, it can be drawn, it can be serialized, etc). Mixins in Python just so happen to be implemented by adding base classes.
Inheritance itself isn’t really a problem. It usually only matters when you have unnecessarily deep hierarchies, where a change in a base class can change functionality in dozens of classes in an unintentional way. Similarly, it can add complexity once the hierarchy is deep enough, but only really if you throw too much into the base classes.
Python’s ABCs are more of interfaces though, which is why despite Python using base classes to “inherit” them, a lot of that is really composition (or putting a class together from parts) rather than inheriting and overriding implementation details from a parent/grandparent/etc type.
Great article.
A lot of people are on the “composition over inheritance” bandwagon now, but I’ve honestly not seen a situation where I felt that inheritance was used and was the wrong choice. (Though most of my experience is in python where there’s no diamond problem, mixin classes are common, etc)
What I noticed is that everyone seems to agree that inheriting implementation is useful, because you have that with traits in rust (which are agreed to be good, afaik), so in languages without traits, it seems reasonable to want to use the next best thing
Mixins are composition! They don’t describe what a type is (“circle” is a “shape”, etc) but rather what they can do (“circle” can have its area calculated, it can be drawn, it can be serialized, etc). Mixins in Python just so happen to be implemented by adding base classes.
Inheritance itself isn’t really a problem. It usually only matters when you have unnecessarily deep hierarchies, where a change in a base class can change functionality in dozens of classes in an unintentional way. Similarly, it can add complexity once the hierarchy is deep enough, but only really if you throw too much into the base classes.
Python’s ABCs are more of interfaces though, which is why despite Python using base classes to “inherit” them, a lot of that is really composition (or putting a class together from parts) rather than inheriting and overriding implementation details from a parent/grandparent/etc type.
My feeling was always that it was deep hierarchies that were the real problem. But people don’t always articulate it that way!