01-generic-methods.go

package main

type Addable interface {
	Total int
	Add(value int) int
}

func (addable *Addable) Add(value int) int {
	addable.Total = addable.Total + value

	return addable.Total
}

type Order struct {
	Total int
}

func main() {
	order := &Order{ Total: 0 }
	order.Add(1)

	fmt.Println(order.Total)
}

02-overriding-generic-methods.go

package main

type Addable interface {
	Total int
	Add(value int) int
}

func (addable *Addable) Add(value int) int {
	addable.Total = addable.Total + value

	return addable.Total
}

type Order struct {
	Total int
}

func (order *Order) Add(value int) int {
	if value <= 3 {
		addable.Total = addable.Total + value
	}

	return addable.Total
}

func main() {
	order := &Order{ Total: 0 }
	order.Add(1)

	fmt.Println(order.Total)
}