Swift Equatable on a protocol

Question

I don\'t think this can be done but I\'ll ask anyway. I have a protocol:

protocol X {}

And a class:

class Y:X {}

Answer 1

Not sure why you need all instances of your protocol to conform to Equatable, but I prefer letting classes implement their equality methods.

In this case, I'd leave the protocol simple:

protocol MyProtocol {
    func doSomething()
}

If you require that an object that conforms to MyProtocol is also Equatable you can use MyProtocol & Equatable as type constraint:

// Equivalent: func doSomething(element1: T, element2: T) where T: MyProtocol & Equatable {
func doSomething(element1: T, element2: T) {
    if element1 == element2 {
        element1.doSomething()
    }
}

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This way you can keep your specification clear and let subclasses implement their equality method only if required.