Swift Array.contains() doesn't call Equatable function of PFUser subclass

I have a subclass of PFUser - MYUser class with implementation of Equatable function for comparing objectIds this way:

func ==(left: MYUser, right: MYUser) -> Bool {
    return left.objectId == right.objectId
}

But when I call Array.contains() method it doesn't call this implementation of Equatable function, that leads to incorrect results. For instance, here:

let hasUser = self.selectedUsers.contains(currentUser)

hasUser becomes false if selectedUsers array contains different memory object but with the same objectId as in currentUser.

What interesting, Equatable function implementation is called in direct usage. Here:

var hasUser = false
for itUser in self.selectedUsers {
  if itUser == currentUser {
    hasUser = true
    break
  }
}

== operator successfully was called and hasUser has correct values for different memory objects but with the same objectId

What can be the cause of it?

UPDATE. Here is MYUser class:

class MYUser: PFUser {

    // MARK: - Parse Object

    @NSManaged var avatarFile: PFFile?
    @NSManaged var fullName: String?

    // MARK: - PFSubclassing Methods (through PFUser)

    override class func initialize() {
        struct Static {
            static var onceToken : dispatch_once_t = 0;
        }
        dispatch_once(&Static.onceToken) {
            self.registerSubclass()
        }
    }
}

func ==(left: MYUser, right: MYUser) -> Bool {
    return left.objectId == right.objectId
}

I think is this a NSObject issue.

class MYUserNSObject: NSObject {
    dynamic var fullName: String

    init(fullName: String) {
        self.fullName = fullName
        super.init()
    }
}

func ==(left: MYUserNSObject, right: MYUserNSObject) -> Bool {
    return left.fullName == right.fullName
}

let objectUsers = [MYUserNSObject(fullName: "a"), MYUserNSObject(fullName: "b")]
let objectResult = objectUsers.contains(MYUserNSObject(fullName: "a"))
print("\(result)")

Prints false.

class MYUserSwift: Equatable {
    var fullName: String

    init(fullName: String) {
        self.fullName = fullName
    }
}

func ==(left: MYUserSwift, right: MYUserSwift) -> Bool {
    return left.fullName == right.fullName
}

let swiftUsers = [MYUserSwift(fullName: "a"), MYUserSwift(fullName: "b")]
let swiftResult = swiftUsers.contains(MYUserSwift(fullName: "a"))
print("\(swiftResult)")

Prints true.

---

Finally, by adding -isEqual:, I fixed this.

class MYUserNSObject: NSObject {
    dynamic var fullName: String

    init(fullName: String) {
        self.fullName = fullName
        super.init()
    }

    override func isEqual(object: AnyObject?) -> Bool {
        guard let user = object as? MYUserNSObject else { return false }
        return self == user
    }
}

func ==(left: MYUserNSObject, right: MYUserNSObject) -> Bool {
    return left.fullName == right.fullName
}

let objectUsers = [MYUserNSObject(fullName: "a"), MYUserNSObject(fullName: "b")]
let objectResult = objectUsers.contains(MYUserNSObject(fullName: "a"))
print("\(objectResult)")

Prints true.

---

Updated for Swift 4.0

class MYUserNSObject: NSObject {
    @objc var fullName: String

    init(fullName: String) {
        self.fullName = fullName
        super.init()
    }

    override func isEqual(_ object: Any?) -> Bool {
        guard let user = object as? MYUserNSObject else { return false }
        return self.fullName == user.fullName
    }
}

let objectUsers = [MYUserNSObject(fullName: "a"), MYUserNSObject(fullName: "b")]
let objectResult = objectUsers.contains(MYUserNSObject(fullName: "a"))
print("\(objectResult)")

Prints true.

Note: there is no longer a ==(left:right:) function needed.

let success = MYUserNSObject(fullName: "a") == objectUsers[0]
print("success should be true: \(success)")

let failure = MYUserNSObject(fullName: "a") == objectUsers[1]
print("failure should be false: \(failure)")