an unexpected error while writing a piece of code from Swift programming by Apple(optional chaining)

Question

I wrote the following piece of code which is identical to Swift Programming Language by Apple and got an unexpected error saying : type'()' does not conform to protocol 'boolean type' , its location is shown in the following code:

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

You need to add spaces around your != operators.

Change:

if buildingName!=nil

To:

if buildingName != nil

Swift is parsing buildingName!=nil as buildingName! = nil, so help it out by adding spaces around the boolean operator.