Go Inheritance and Polymorphism

Internal

• Go Object Oriented Programming

Overview

Go does not have formal inheritance at language level. Inheritance can be implemented via a combination of struct field embedding and interfaces. The Inheritance section of this article explains how that is done. Once an implicit inheritance structure is put in place, polymorphism is also available.

Inheritance

In its most generic form, inheritance in programming languages is the capability of declaring class hierarchies. A hierarchy includes generic classes, called superclasses, that are inherited by more specific and specialized classes, called subclasses.

The superclasses declare attributes (state) and behavior that are shared with all their descendants. This is a great capability when it comes to code reusability. The generic state and behavior is declared only once, in superclass, and it does not have to be repeated in subclasses. The subclasses also have the capability to declare state and behavior that is particular to them only, and differentiate them from siblings in the hierarchy. For more general information on inheritance see:

Inheritance

Inheritance as defined above ca be implemented in Go, but without formal support from the language. State inheritance is implemented using struct embedding. Behavior inheritance is implemented using interfaces.

Example Hierarchy

We use an example hierarchy involving vehicles. The base type, and the specialized types are declare in their own source files, in the same transportation package:

 pkg
  └── transportation
       ├── vehicle.go
       ├── car.go
       └── plane.go

State Inheritance

We implement state inheritance with struct embedding. We declare a base struct that contains all the attributes to be shared by inherited types. In this case, in a vehicle hierarchy, the base type is vehicle and it is declared package-private, as it does not need exposure outside the package. It contains fields that are common to all members of the hierarchy, like speed, for example:

package transportation

type vehicle struct {
	speed int
}

All sub-types, like a Car or a Plane, have a speed, which is not needed to be declared when we declared the corresponding types, as long as we embed the base type vehicle:

package transportation

type Car struct {
	vehicle
}

package transportation

type Plane struct {
	vehicle
}

Note that Car and Plane are exported, presumably we need to use these types outside the package, unlike the base type vehicle.

Polymorphism

Polymorphism is available in Go, but it is implemented differently than in other object-oriented languages.

For a generic discussion on polymorphism, see:

Object-Oriented Programming | Polymorphism

TO DEPLETE

Read and merge into document:

• https://go.dev/doc/faq#Is_Go_an_object-oriented_language