advanced-go-programming-book/examples/ch2-05/class-go2cc/goobj.go

package main

import (
	"sync"
)

type ObjectId int32

var refs struct {
	sync.Mutex
	objs map[ObjectId]interface{}
	next ObjectId
}

func init() {
	refs.Lock()
	defer refs.Unlock()

	refs.objs = make(map[ObjectId]interface{})
	refs.next = 1000
}

func NewObjectId(obj interface{}) ObjectId {
	refs.Lock()
	defer refs.Unlock()

	id := refs.next
	refs.next++

	refs.objs[id] = obj
	return id
}

func (id ObjectId) IsNil() bool {
	return id == 0
}

func (id ObjectId) Get() interface{} {
	refs.Lock()
	defer refs.Unlock()

	return refs.objs[id]
}

func (id ObjectId) Free() interface{} {
	refs.Lock()
	defer refs.Unlock()

	obj := refs.objs[id]
	delete(refs.objs, id)

	return obj
}