Chapter 11 — Advanced OOP: abstract, mixins, enums

Level: intermediate Estimated time: 7 h Prerequisites: Chapter 10 — Encapsulation, inheritance, polymorphism What you will be able to do by the end: design a clean class hierarchy with abstract classes, interfaces, mixins, enums, and extensions, and choose the right tool for each need.

11.0 — Chapter objectives

By the end of this chapter, you will be able to:

• explain why single inheritance is not always enough;
• understand what an abstract class is;
• use the abstract keyword;
• write an abstract method, that is, a method without a body;
• understand why an abstract class cannot be instantiated;
• mix concrete and abstract methods in the same class;
• understand the notion of an implicit interface, specific to Dart;
• use the implements keyword;
• clearly distinguish extends from implements;
• implement several interfaces on a single class;
• explain the problem that mixins solve;
• declare a mixin and apply it with with;
• apply several mixins and understand the resolution order;
• restrict a mixin with the on keyword;
• declare and use an enum;
• write a switch on an enum;
• use values, index, and name;
• write an enhanced enum with properties and methods;
• add features to an existing type with extension ... on;
• choose between composition and inheritance;
• know which tool to use for which need.