swift - 继承符合协议(protocol)的类

Question

我不明白为什么 Xcode Playground 崩溃，这是我的基本设置

protocol Shootable {
    func shoot()
}

class BaseMissile: Shootable {

    var damage = 0

    func shoot() {
        println("Pew pew for \(damage) damage")
    }
}

class Missile1: BaseMissile {

    override init() {
        super.init()
        damage = 1
    }

}

protocol Targetable {
    var life: Int {get set}
}

class BaseSpaceship: Targetable {

    var life = 0
    var currentMissile: BaseMissile!

    func printHealth() {
        println("My current life: \(life)")
    }

}

class Spaceship1: BaseSpaceship {


    override init() {
        super.init()
        life = 1
        currentMissile = Missile1()
    }
}

var spaceship = Spaceship1()
spaceship.printHealth()
spaceship.currentMissile.shoot()

特别是最后一行spaceship.currentMissile.shot()导致 Playground 崩溃。如果我将 var currentMissile: BaseMissile! 从 BaseSpaceship 移动到 Spaceship1 它可以工作，但这是处理此问题的可接受方法吗？

Answer 1

我猜发生这种情况是因为 BaseSpaceship 类没有初始化器，并且 var currentMissile: BaseMissile! 不能为零。所以你要么应该通过替换来选择它!和 ？或者给它一个默认值。