Swift闭包变量捕获趣味题

题目一

var car = "大奔"
let block = { (car: String) in
    print("我开\(car)")
}
car = "雅迪"
block(car)

block的参数是外界传入的，调用时block传入的参数值为"雅迪"，所以答案为我开雅迪

题目二

var car = "大奔"
let block = { [ car ] in
    print("我开\(car)")
}
car = "雅迪"
block()

block在调用之前，将car捕获为自身局部变量，捕获时car的值为"大奔"，所以答案为我开大奔

题目三

var car = "大奔"
let block = {
    print("我开\(car)")
}
car = "雅迪"
block()

block没有对car进行复制，所以block内部的car还是全局的car变量，所以答案为我开雅迪

题目四

class Car {
    var name: String = ""
}
var car = Car()
car.name = "大奔"
let block = { [ car ] in
    print("我开\(car?.name)")
}
car.name = "雅迪"
block()

block在调用之前，将car捕获为自身的局部变量，但是car的name属性为指针类型，所以答案为我开雅迪

题目五

在题目四的基础上，在name重新赋值前，更新car的指针指向，即

class Car {
    var name: String = ""
}
var car = Car()
car.name = "大奔"
let block = { [ car ] in
    print("我开\(car.name)")
}
car = Car()
car.name = "雅迪"
block()

block在调用之前，将car捕获为自身的局部变量，又因为car在block调用之前就被重新赋值，所以block捕获的car与外界的car不是同一个，block捕获的car还是car在第二次赋值前的那个，即name="大奔"。所以答案为我开大奔

题目六

在题目五的基础上，捕获的car用weak修饰，即

class Car {
    var name: String = ""
}
var car = Car()
car.name = "大奔"
let block = { [ weak car ] in
    print("我开\(car?.name)")
}
car = Car()
car.name = "雅迪"
block()

如题五的解释的基础上，因为捕获的car为弱引用类型，所以此时car在block中相当于做了一次浅拷贝，在car被重新赋值时，原指针被销毁。所以答案为我开nil