我创建了一些样例项目来测试各种类型的变量实现,以测试哪些变量只执行一次,哪些变量每次调用都执行。
class Something:NSObject
{
var clock:Int = 0
override var description: String
{
let desc = super.description
clock += 1
return "\(desc) Clock: \(clock)"
}
}
static var staticVar:Something
{
print("static Var")
return Something()
}
static var staticVar2:Something = {
print("static Var II")
return Something()
}()
lazy var lazyVar:Something = {
print("lazy Var")
return Something()
}()
var simpleVar:Something {
print("simple Var")
return Something()
}
var simpleVar2:Something = {
print("simple Var II")
return Something()
}()
接着在viewDidLoad()
(确保变量已经初始化),将所有变量调用几次并保存在数组中以保持引用强度。
var strongArr = [Something]()
print("== STATIC VAR")
strongArr.append(ViewController.staticVar)
print(strongArr.last!.description)
strongArr.append(ViewController.staticVar)
print(strongArr.last!.description)
strongArr.append(ViewController.staticVar)
print(strongArr.last!.description)
print("\n== STATIC VAR {}()")
strongArr.append(ViewController.staticVar2)
print(strongArr.last!.description)
strongArr.append(ViewController.staticVar2)
print(strongArr.last!.description)
strongArr.append(ViewController.staticVar2)
print(strongArr.last!.description)
print("\n== SIMPLE VAR")
strongArr.append(self.simpleVar)
print(strongArr.last!.description)
strongArr.append(self.simpleVar)
print(strongArr.last!.description)
strongArr.append(self.simpleVar)
print(strongArr.last!.description)
print("\n== SIMPLE VAR {}()")
strongArr.append(self.simpleVar2)
print(strongArr.last!.description)
strongArr.append(self.simpleVar2)
print(strongArr.last!.description)
strongArr.append(self.simpleVar2)
print(strongArr.last!.description)
print("\n== LAZY VAR {}()")
strongArr.append(self.lazyVar)
print(strongArr.last!.description)
strongArr.append(self.lazyVar)
print(strongArr.last!.description)
strongArr.append(self.lazyVar)
print(strongArr.last!.description)
这是在控制台中记录的结果
== STATIC VAR
static Var
<_TtCC8DemoDemo14ViewController9Something: 0x600003725100> Clock: 1
static Var
<_TtCC8DemoDemo14ViewController9Something: 0x600003725160> Clock: 1
static Var
<_TtCC8DemoDemo14ViewController9Something: 0x600003725270> Clock: 1
== STATIC VAR {}()
static Var II
<_TtCC8DemoDemo14ViewController9Something: 0x6000037251b0> Clock: 1
<_TtCC8DemoDemo14ViewController9Something: 0x6000037251b0> Clock: 2
<_TtCC8DemoDemo14ViewController9Something: 0x6000037251b0> Clock: 3
== SIMPLE VAR
simple Var
<_TtCC8DemoDemo14ViewController9Something: 0x600003725240> Clock: 1
simple Var
<_TtCC8DemoDemo14ViewController9Something: 0x6000037252a0> Clock: 1
simple Var
<_TtCC8DemoDemo14ViewController9Something: 0x6000037252b0> Clock: 1
== SIMPLE VAR {}()
<_TtCC8DemoDemo14ViewController9Something: 0x600003738100> Clock: 1
<_TtCC8DemoDemo14ViewController9Something: 0x600003738100> Clock: 2
<_TtCC8DemoDemo14ViewController9Something: 0x600003738100> Clock: 3
== LAZY VAR {}()
lazy Var
<_TtCC8DemoDemo14ViewController9Something: 0x60000372ea70> Clock: 1
<_TtCC8DemoDemo14ViewController9Something: 0x60000372ea70> Clock: 2
<_TtCC8DemoDemo14ViewController9Something: 0x60000372ea70> Clock: 3
根据这些测试结果,看起来如果两者都定义为闭包(在结尾处加上()
),那么懒惰变量和简单变量之间没有区别。
将变量实现为闭包是否自动使变量成为懒惰变量,还是我漏掉了什么?