swift - 不能赋值，Swift 对待是不可变的

Question

我有协议(protocol):

protocol CellLineDrawing : Any {
    var isShouldDrawBottomLine : Bool { get set  }
    var isShouldDrawUpperLine : Bool { get set }
}

然后我尝试为符合协议(protocol)的对象设置值:

var arrValues : [Any]!


func drawLinesIfNeeded () -> Void {

    guard arrValues!.count > 0 else {
        print("Empty array")
        return
    }

    guard arrValues!.first is CellLineDrawing else {
        print("Does not conform to cell line drawing protocol")
        return
    }

    var firstModel = arrValues.first
    var lastModel = arrValues.last

    (firstModel as! CellLineDrawing).isShouldDrawUpperLine = true //ERROR - Cannot assign to immutable expression of type 'Bool'




}

Answer 1

表达式 (firstModel as!CellLineDrawing) 是一个常量，你不能改变它的属性(除非它是引用类型)。

除非我弄错了，否则你需要一个临时变量:

if var firstModel = arrValues.first as? CellLineDrawing {
    firstModel.isShouldDrawUpperLine = true
    arrValues[0] = firstModel
}