Embedded struct

Go is not an object-oriented language. However, embedded structs provide a kind of data-only inheritance that can be useful at times. Keep in mind, Go doesn't support classes or inheritance in the complete sense, embedded structs are just a way to elevate and share fields between struct definitions.

type car struct {
  make string
  model string
}

type truck struct {
  // "car" is embedded, so the definition of a
  // "truck" now also additionally contains all
  // of the fields of the car struct
  car
  bedSize int
}

• An embedded struct's fields are accessed at the top level, unlike nested structs.

• Promoted fields can be accessed like normal fields except that they can't be used in composite literals

lanesTruck := truck{
  bedSize: 10,
  car: car{
    make: "toyota",
    model: "camry",
  },
}

fmt.Println(lanesTruck.bedSize)

// embedded fields promoted to the top-level
// instead of lanesTruck.car.make
fmt.Println(lanesTruck.make)
fmt.Println(lanesTruck.model)

STRUCT METHODS IN GO

While Go is not object-oriented, it does support methods that can be defined on structs. Methods are just functions that have a receiver. A receiver is a special parameter that syntactically goes before the name of the function.

type rect struct {
  width int
  height int
}

// area has a receiver of (r rect)
func (r rect) area() int {
  return r.width * r.height
}

r := rect{
  width: 5,
  height: 10,
}

fmt.Println(r.area())
// prints 50

A receiver is just a special kind of function parameter. Receivers allow us to define interfaces that structs (and other types) can implement.