main.go

/*

Golang's methods are not "virtual" or "overridable".
Don't expect OOP-like inheritance, use composition instead.

Try it here: https://play.golang.org/p/DujbnuHDZAW

*/

package main
import "fmt"

type Node interface {
	GetID() string
	Print()
}


/* THIS IS WRONG */

type BasicNodeWrong struct {
}

func (n BasicNodeWrong) Print() {
	fmt.Printf("My ID is %s\n", n.GetID())
}

func (n BasicNodeWrong) GetID() string {
	return "[Internal error - GetID called on BasicNodeWrong]"
}


type SpecialNodeWrong struct {
	*BasicNodeWrong
	ID string
}

func (n SpecialNodeWrong) GetID() string {
	return n.ID
}

func NewSpecialNodeWrong(ID string) *SpecialNodeWrong {
	return &SpecialNodeWrong{
		&BasicNodeWrong{},
		ID,
	}
}


/* THIS IS RIGHT */

type Identifier interface {
	GetID() string
}

type BasicIdentifier struct {
	ID string
}

func (id BasicIdentifier) GetID() string {
	return "basic:"+id.ID
}

type SpecialIdentifier struct {
	*BasicIdentifier
}

func (id SpecialIdentifier) GetID() string {
	return "special:"+id.ID
}

type NodeRight struct {
	ID Identifier
}

func (n NodeRight) GetID() string {
	return n.ID.GetID()
}

func (n NodeRight) Print() {
	fmt.Printf("My ID is %s\n", n.ID.GetID())
}

func NewBasicNode(ID string) *NodeRight {
	return &NodeRight{
		&BasicIdentifier{ID},
	}
}

func NewSpecialNode(ID string) *NodeRight {
	return &NodeRight{
		&SpecialIdentifier{&BasicIdentifier{ID}},
	}
}





func main() {
	var n Node = NewSpecialNodeWrong("1")
	n.Print()

	var bn Node = NewBasicNode("2")
	bn.Print()

	var sn Node = NewSpecialNode("3")
	sn.Print()
}