从 Apple 的 Swift 编程编写一段代码时出现意外错误（可选链接）

Question

我编写了以下与 Apple 的 Swift Programming Language 相同的代码，但出现意外错误： type'()' does not conform to protocol 'boolean type' ，其位置显示在以下代码中：

class Person1 {
    var residence:Residence?
}

class Residence {
var rooms=[Room]()
var numberOfRooms:Int{
return rooms.count
}
subscript(i:Int)->Room{
    get{
        return rooms[i]
    }
    set{
        rooms[i]=newValue
    }
}
func printNumberOfRooms(){
    println("the number of rooms is \(numberOfRooms)")
}
var address:Address?
}
class Room {
var name:String
init(name:String){
    self.name=name
}
}
class Address {
var builingNumber:String?
var buildingName:String?
var street:String?
func buildingIdentifier()->String?{
    if buildingName!=nil {return buildingName}  Error:type'()' does not conform to   protocol 'boolean type'
    else if builingNumber!=nil {return builingNumber}
    else {return nil}
}
}

Answer 1

您需要在 != 运算符周围添加空格。

变化：

if buildingName!=nil

收件人：

if buildingName != nil

Swift 将 buildingName!=nil 解析为 buildingName! = nil，因此请在布尔运算符周围添加空格。