Custom equality in swift objects preserving compatibility with legacy Objective-C code

equality, swift

Solution

Yes, you need to override `isEqual` (and `hash`) to make your objects fully Objective-C compatible. Here's a Playground-ready example for the syntax:

import Foundation

class MyClass: NSObject {

    var value = 5

    override func isEqual(object: AnyObject?) -> Bool {
        if let object = object as? MyClass {
            return value == object.value
        } else {
            return false
        }
    }

    override var hash: Int {
        return value.hashValue
    }
}

var x = MyClass()
var y = MyClass()
var set = NSMutableSet()

x.value = 10
y.value = 10
set.addObject(x)

x.isEqual(y) // true
set.containsObject(y) // true

(syntax current as of Xcode 6.3)

Problem

In Objective-C you would do something along the lines of ``` - (BOOL)isEqual:(id)other { if (other == self) return YES; if (!other || ![other isKindOfClass:[self class]]) return NO; return [self.customProperty isEqual:other.customProperty]; } ``` My first naive attempt in swift goes as follows ``` func isEqual(other: AnyObject) -> Boolean { if self === other { return true } if let otherTyped = other as? MyType { return self.myProperty == otherTyper.myProperty } return false } ``` But I'm far from being happy with it. I don't even know whether the signature is right or whether we're supposed to use anything different than `isEqual`. Any thoughts? EDIT: I'd also like to keep Objective-C compatibility (my class is used in both legacy Obj-C code and new Swift code). So I think only overriding `==` isn't enough. Am I wrong?

Original source