lazyload.go

package main

import "fmt"

type Unit struct {
	ID   int
	Name string
}

type Player struct {
	unit *UnitLazy
}

func NewPlayer() *Player {
	return &Player{
		unit: NewUnitLazy(getUnit),
	}
}

func (p *Player) Unit() *Unit {
	return p.unit.Get()
}

func getUnit() *Unit {
	fmt.Println("Get Unit")
	return &Unit{1, "hoge"}
}

func main() {
	p := NewPlayer()
	unit := p.Unit()
	fmt.Println(unit)
	unit = p.Unit()
	fmt.Println(unit)
}

type Lazy struct {
	v      interface{}
	getter func() interface{}
}

func NewLazy(getter func() interface{}) *Lazy {
	return &Lazy{
		getter: getter,
	}
}

func (l *Lazy) Get() interface{} {
	if l.v != nil {
		return l.v
	}
	v := l.getter()
	l.v = v
	return v
}

type UnitLazy struct {
	*Lazy
}

func (ul *UnitLazy) Get() *Unit {
	return ul.Lazy.Get().(*Unit)
}

func NewUnitLazy(getter func() *Unit) *UnitLazy {
	return &UnitLazy{
		NewLazy(func() interface{} {
			return getter()
		}),
	}
}