Interfaces, abstract classes, and mixins

In Dart, abstract classes and interfaces are closely related to one another. This is because Dart implements interfaces in a subtly different way from most typical languages.

Let's take a look at abstract classes first before linking them to the topic of implicit interfaces.

Abstract classes

In OOP, abstract classes are classes that cannot be instantiated, which makes a lot of sense, depending on the context and the level of abstraction in a program.

For example, our Person class could be abstract if we want to make sure that it only exists in the context of the program if it is a Student instance or another subtype:

abstract class Person {
  // ... the body was hidden for brevity...