How to compare Equatables

Using Swift
1

Hi there,

I have a question. How can I compare Any objects when they are actually Equatable? If it happens to be Hashable, I can use AnyHashable just like the sample below, but there's not such thing as AnyEquatable. What's the recommended way?

struct Person {
  let age: Int
  let name: String
}

func test<T: Equatable>(_ p1: Person, _ p2: Person, _ k: KeyPath<Person, T>) -> Bool {
  return p1[keyPath: k] == p2[keyPath: k]
}

func test(_ p1: Person, _ p2: Person, _ arr: [PartialKeyPath<Person>]) -> Bool {
  for k in arr {
    if let h1 = p1[keyPath: k] as? AnyHashable, let h2 = p2[keyPath: k] as? AnyHashable {
      if h1 != h2 { return false }
    } else {
      // how am I supposed to compare them?
    }
  }
  return true
}

let bob = Person(age: 42, name: "bob")
let jon = Person(age: 42, name: "jon")

test(bob, jon, \.age)  // true
test(bob, jon, [\Person.age, \Person.name])  // can't omit Person but besides the point

Should I implement AnyEquatable just like AnyHashable? I'm not familiar with the magic behind downcasting but can I implement so that I should be able to make "foo as? AnyEquatable" work?

2

The easiest thing to do would be to require Hashable and use AnyHashable. It is not possible to extend downcasting to implement your own AnyEquatable type.

3

Darnit. I have a type which is Equatable but not Hashable was the reason I posted my question.

So, why don't we have AnyEquatable? Is it not possible to implement even in stdlib? Don't we want it?