Question

我正在关注先进的swift WWDC 2014视频，使用类上的下标委托给一个类属性，但是我使用与视频相同的语法收到错误

enum Direction {
    case North, South, East, West
}

class Place: Thing {
    init (_ location: Thing?, _ name: String, _ longDescription: String) {
        self.exits = Dictionary<Direction, Place> ()
        super.init(location, name, longDescription)
    }
    var exits: Dictionary<Direction, Place>
}

extension Place {
    subscript(direction: Direction) -> Place? {
        get {
            return exits[direction]
        }
        set (destination: Place?) { // error here
            exits[direction] = destination
        }
    }
}

我得到的错误是

Expected '{' to start setter definition

Answer 1

省略你的setter中的类型，它会自动推断：

subscript(direction: Direction) -> Place? {
    get {
        return exits[direction]
    }
    set (destination) {
        exits[direction] = destination
    }
}

您也可以完全跳过参数，在这种情况下，它隐式命名为newValue：

subscript(direction: Direction) -> Place? {
    get {
        return exits[direction]
    }
    set {
        exits[direction] = newValue
    }
}

Answer 2

不要传递参数来设置

set  { 
    exits[direction] = newValue
}

斯威夫特 - 期待＆＃39; {＆＃39;启动setter定义

2 个答案: