interfaces and type embedding golang

embed_interface.go

package main

import "fmt"

type Boss struct{}

func (b *Boss) AssignWork() {
	fmt.Println("Boss assigned work")
}

type Manager struct{}

func (m *Manager) PreparePowerPoint() {
	fmt.Println("Power point prepared")
}

type BossManager struct {
	Boss
	Manager
}

type BossManagerUsingPointer struct {
	*Boss
	*Manager
}

type PromotionalMaterail interface {
	AssignWork()
	PreparePowerPoint()
}

func promote(pm PromotionalMaterail) {
	fmt.Println("Promoted a person with promise")
}

func main() {
	bm := BossManager{}

	//Both methods which uses pointer receivers have been promoted
	//to BossManager
	bm.AssignWork()
	bm.PreparePowerPoint()

	// However, the method set of BossManager does not invlude either
	// method because:
	// 1) {Boos, Manager} are embedded as value types, not pointer types.
	// 2) This makes it so that only the pointer type *BoosManager
	// includes both methods in its method set, thus making it implement
	// interface PromotionMaterial

	// promote(bm) // would fail withy: can not use bm(type BossManager)
	// as type PromotionMaterial in argument to promote:
	//BoosManager does not implement PromotionMaterial (AssignWork method
	// has pointer receiver)
	// This Would work if {Boss, Manager} were embedded as pointer types.

	promote(&bm) // Works

	// Let us use the struct with the embedded pointer types:
	bm2 := BossManagerUsingPointer{}
	bm2.AssignWork()
	bm2.PreparePowerPoint()
	promote(bm2)
	promote(&bm2)
}