Swift, how to implement Hashable protocol based on object reference?

Question

I\'ve started to learn swift after Java. In Java I can use any object as a key for HashSet, cause it has default hashCode and equals based on objec

Answer 1

Another option is to implement an extension to Hashable and Equatable protocols for AnyObject. It seems to achieve a similar effect as the one you mentioned in Java.

It adds a default behavior to all classes within your project and is not necessary the better option compared to adding such behavior to only a designated class. So, I am just mentioning it for the sake of completeness:

class HashableClass: Hashable {


}

extension Hashable where Self: AnyObject{

  func hash(into hasher: inout Hasher) {

     hasher.combine(ObjectIdentifier(self))
   }
}


extension Equatable where Self: AnyObject{

   static func ==(lhs: Self, rhs: Self) -> Bool {
      return lhs === rhs
   }
}

Now, if you you would like to implement specific logic for your class, you could still do that, like this:

class HashableClass { //deleted the Hashable conformance


}
extension HashableClass : Hashable{

   func hash(into hasher: inout Hasher) {

      //your custom hashing logic
   }
}

To avoid adding default behavior to AnyObject, another protocol can be declared and extension relevant only to this new protocol can be added:

protocol HashableClass : AnyObject{

}

class SomeClass: Hashable, HashableClass {


 }

 extension Hashable where Self: HashableClass{

   func hash(into hasher: inout Hasher) {

      hasher.combine(ObjectIdentifier(self))
   }
 }


extension Equatable where Self: HashableClass{

   static func ==(lhs: Self, rhs: Self) -> Bool {
     return lhs === rhs
   }
}