Swift NSObject子类符合Objective-C协议的问题

Question

This piece of code works absolutely fine in Swift 1.1

// Obj-C

@import Foundation;

@protocol HashableObject <NSObject>
- (NSUInteger)hash;
@end

// Swift

import Foundation

@objc class Object: NSObject, HashableObject {

    func hash() -> UInt {
        return 0
    }
}

However, in latest Swift 1.2 and XCode 6.3beta2 the compiler complains that Method 'hash()' overrides Objective-C method 'hash' from superclass 'NSObject'

Is that a bug, or something else has fundamentally changed and the code is wrong? Are there any workarounds to this? I have numerous things in my code that need to conform to certain protocols from Objective-C libraries and this essentially breaks everything with no apparent solution other than wait for the next Swift release.

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
    }
}