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Inheritance and subclassing in Go - or its near likeness
Now what does this mean for us in programming? Assume you had the class
Car
and it has a member method called numberOfWheels()
. If we create a subclass Ferrari
of Car
, what it means in coding is that we should automatically have a Ferrari.numberOfWheels()
- i.e. the subclass gets the super class’ behaviors or its methods.With what we’ve learnt already with Anonymous fields in structs and Methods on structs, we can achieve the same paradigm in Go. If, like me, you have been more used to object oriented programming so far, a couple of examples will help explain how.
Full code
package main import "fmt" type Car struct { wheelCount int } // define a behavior for Car func (car Car) numberOfWheels() int { return car.wheelCount } type Ferrari struct { Car //anonymous field Car } func main() { f := Ferrari{Car{4}} fmt.Println("A Ferrari has this many wheels: ", f.numberOfWheels()) //no method defined for Ferrari, but we have the same behavior as Car. }
In the above program, we have only defined a method or behavior for
Car
. Since we then defined Car
as an anonymous field in Ferrari
, the latter class automatically can call on all the visible behaviors/methods of the anonymous field type. So here, we have not subclassed a parent class, but composed it. But the effect is the very same - you have all the behaviors of the parent with none of the frills of object oriented programming. C’mon, you have to agree with me that that is cool! Let’s bring in the Aston Martin also now, and this time add some individual behavior in addition to that inherited.Full code
package main import "fmt" type Car struct { wheelCount int } func (car Car) numberOfWheels() int { return car.wheelCount } type Ferrari struct { Car } // a behavior only available for the Ferrari func (f Ferrari) sayHiToSchumacher() { fmt.Println("Hi Schumacher!") } type AstonMartin struct { Car } // a behavior only available for the AstonMartin func (a AstonMartin) sayHiToBond() { fmt.Println("Hi Bond, James Bond!") } func main() { f := Ferrari{Car{4}} fmt.Println("A Ferrari has this many wheels: ", f.numberOfWheels()) //has car behavior f.sayHiToSchumacher() //has Ferrari behavior a := AstonMartin{Car{4}} fmt.Println("An Aston Martin has this many wheels: ", a.numberOfWheels()) //has car behavior a.sayHiToBond() //has AstonMartin behavior }
Hi Schumacher!
An Aston Martin has this many wheels: 4
Hi Bond, James Bond!
In the above program, both the Aston Martin and the Ferrari, behave like a car - since both can access the
numOfWheels
method from Car
as if it was directly available in it. In addition, it defines its own behaviors that only itself can use. So the neither the Car
nor the AstonMartin
can call sayHiToSchumacher
; similarly only the AstonMartin
can call sayHiToBond
and neither Ferrari
nor Car
can do that.In short, by using Go’s concept of anonymous fields, we arrive at the same concept as subclassing and inheritance. It would appear inside out at first that to subtype something, you put the parent type within the sub type.