Go structs and interfaces

2015-10-11

Go doesn’t have a class to define custom types. Instead, you would use a struct.

type MotorVehicle struct {
    wheelSize int
    modelName string
    manafacturer string
}

Then, to add method to this type, we would just implement methods against this type as described on our previous post.

func (mv MotorVehicle) startEngine(){

    fmt.Printf("Starting %s's engine\n", mv.modelName)

}

Multiple inheritance can be achieved by type embedding.

type Car struct {
    MotorVehicle
    //otherFields
}

When type embedding, the fields (and methods of the parent type) can be referenced without sub-referencing the embedded type (assuming you don’t overload that same field names). This of course only works when adding an anonymous field (not giving the embedded type a name) to the struct. So, using the above example, we could do:

var mazdaCx9 Car
mazdaCx9.wheelSize = 17
//or
mazdaCx9.MotorVehicle.wheelSize = 17

To implement an interface is go, you firstly define the interface as a type (similar to how a struct is defined). Whereas struct’s can only house fields, interfaces can only house function specifications.

type PoweredVehicle interface {
    startEngine()
}

So, with that, any type that implements the method startEngine, becomes a PoweredVehicle. Then we can pass any derived types as a PoweredVehicle type to call any supporting methods.

func goToShops(pv PoweredVehicle){
    pv.startEngine()
    //further implementation
}

myCar := MotorVehicle{}
myCar.wheelSize = 11
myCar.modelName = "abc"
myCar.manafacturer = "def"

goToShops(myCar)