作為一個不稱職的 Swift 工程師，偶爾還是要來了解一下物件的生與死。
我實在是不太想管底層怎麼管理物件的生與死，只要系統幫我自動處理好，我只想要專心在有趣的商業邏輯上。🙃
直接用 Playground 來跑以下程式。
首先定義貓和球，彼此可以互相擁有⋯⋯
class Cat{
var name : String
var age : Int
var ball: Ball?
init(name : String, age : Int) {
self.name = name
self.age = age
print("name:\(name), age:\(age) is initialized")
}
deinit {
print("name:\(name), age:\(age) is deinitialized")
}
}
class Ball{
var owner : Cat
init(owner : Cat) {
self.owner = owner
print("\(owner.name)'s ball is initialized")
}
deinit {
print("\(owner.name)'s ball is deinitialized")
}
}
接下來測試貓和球在什麼時機點誕生與死亡。
１．貓與球一起誕生：
var happyCat : Cat? = Cat(name: "Happy", age: 7)
var happyBall : Ball? = Ball(owner: happyCat!)
輸出：
name:Happy, age:7 is initialized
Happy’s ball is initialized
２．貓誕生與死亡：
var happyCat : Cat? = Cat(name: "Happy", age: 7)
happyCat = nil
輸出：
name:Happy, age:7 is initialized
name:Happy, age:7 is deinitialized
３・貓與球（被貓擁有）誕生，但貓死亡：
var happyCat : Cat? = Cat(name: "Happy", age: 7)
var happyBall : Ball? = Ball(owner: happyCat!)
happyCat = nil
輸出：
name:Happy, age:7 is initialized
Happy’s ball is initialized
４・貓與球（被貓擁有）誕生，接著貓與球死亡：
var happyCat : Cat? = Cat(name: "Happy", age: 7)
var happyBall : Ball? = Ball(owner: happyCat!)
happyCat = nil
happyBall = nil
輸出：
name:Happy, age:7 is initialized
Happy’s ball is initialized
Happy’s ball is deinitialized
name:Happy, age:7 is deinitialized
５・貓（擁有球）與球（被貓擁有）誕生，接著貓與球死亡：
var happyCat : Cat? = Cat(name: "Happy", age: 7)
var happyBall : Ball? = Ball(owner: happyCat!)
happyCat?.ball = happyBall
happyCat = nil
happyBall = nil
輸出：
name:Happy, age:7 is initialized
Happy’s ball is initialized
居然貓和球都設為 nil 了，可是貓和球都還沒死！？😳
Reference Cycle 是指物件是由其他物件組成，當被參考的被參考的物件死亡時，我們觀察記憶體實際上卻沒有釋放空間。
可以怎麼解決此 Memory Leak 問題呢？🤔
參考：
逍遙文工作室 
隨意留個言吧：）～