Overridden == function for Equatable type not called for custom class that subclasses NSCoding and NSObject [duplicate]

Answer 1

Because your class inherits from NSObject you do not need to use the swift protocol Equatable instead you must override the NSObject method isEquals:

Swift 3.x and above

class FooBar: NSObject, NSCoding {
  override func isEqual(_ object: Any?) -> Bool {
    return id == (object as? FooBar)?.id
  }
}

(Thanks to Kamchatka)

Swift 2.x

class FooBar: NSObject, NSCoding {
  override func isEqual(object: AnyObject?) -> Bool {
    return id == (object as? FooBar)?.id
  }
}

Answer 2

You are getting this error because NSObject already conforms to Equatable through its isEqual method.

So I'm not sure if this is the correct way of doing this, but you could override the isEqual method of NSObject:

class FooBar: NSObject, NSCoding {
...

override func isEqual(object: AnyObject?) -> Bool {
    return self == (object as? FooBar)
}