Issue with conforming to Objective-C protocol from Swift NSObject subclass

Question

This piece of code works absolutely fine in Swift 1.1

// Obj-C

@import Foundation;

@protocol HashableObject 
- (NSUInteger)hash;
@end

//          


        

Answer 1

NSObject already has hash property:

protocol NSObjectProtocol {
    var hash: Int { get }

And, Swift 1.2 detects these erroneous overrides. From the release notes:

Swift now detects discrepancies between overloading and overriding in the Swift type system and the effective behavior seen via the Objective-C runtime. (18391046, 18383574)

For example, the following conflict between the Objective-C setter for “property” in a class and the method “setProperty” in its extension is now diagnosed:

class A : NSObject {
  var property: String = "Hello" // note: Objective-C method 'setProperty:’
                                 // previously declared by setter for
                                 // 'property’ here
}
extension A {
    func setProperty(str: String) { } // error: method ‘setProperty’
                                      // redeclares Objective-C method
                                      //'setProperty:’
}

Answer 2

In Swift 1.2 (Xcode 6.3 beta 2) you can override the hash property of NSObject as a computed property:

class Object: NSObject {
    override var hash: Int {
        return 0
    }
}