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 object identifier. How to achieve the same behaviour in Swift?

Answer 1

If you are working with classes and not structs, you can use the ObjectIdentifier struct. Note that you also have to define == for your class in order to conform to Equatable (Hashable requires it). It would look something like this:

class MyClass: Hashable { }  func ==(lhs: MyClass, rhs: MyClass) -> Bool {     return ObjectIdentifier(lhs) == ObjectIdentifier(rhs) }  class MyClass: Hashable {     var hashValue: Int {         return ObjectIdentifier(self).hashValue     } } 

Answer 2

In Swift, the type must conform to Hashable and Equatable for it to be used in a data structure such as a Dictionary or a Set. However, you can add "automatic conformance" by using the "object identifier" of the object. In the code below, I implemented a reusable class to do this automatically.

Note, Swift 4.2 changed how Hashable is implemented, so you no longer override hashValue. Instead, you override hash(into:).

open class HashableClass {     public init() {} }  // MARK: - <Hashable>  extension HashableClass: Hashable {      public func hash(into hasher: inout Hasher) {          hasher.combine(ObjectIdentifier(self))     }          // `hashValue` is deprecated starting Swift 4.2, but if you use      // earlier versions, then just override `hashValue`.     //     // public var hashValue: Int {     //    return ObjectIdentifier(self).hashValue     // } }  // MARK: - <Equatable>  extension HashableClass: Equatable {      public static func ==(lhs: HashableClass, rhs: HashableClass) -> Bool {         return ObjectIdentifier(lhs) == ObjectIdentifier(rhs)     } } 

To use, just take your class and subclass HashableClass, then everything should just work!

class MyClass: HashableClass {  }