Swift 4.2 error: use of unimplemented initializer 'init()' for class

Question

I have a class like this:

class SomeRequest: Hashable {
    let parameter: String

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

    var hashValue: Int {
        return parameter.hashValue
    }
}

Than I try to set value to dictionary by key, where key is SomeRequest:

let request = SomeRequest(parameter: "Some")
let dictionary: [SomeRequest: Any] = [:]
dictionary[request] = ...

After all this I get this error: "use of unimplemented initializer 'init()' for class"

What could be the problem?

Answer 1

Swift 4.2 has changed the protocol Hashable. You can see new func:

public func hash(into hasher: inout Hasher) 

The reason of crash, that hash(into: ) call SomeRequest.init(). You can say: Hey, i don't adopt hash(into: ) method! But swift does behind the scene.

For fix that you need implement hash(into:) :

class SomeRequest: Hashable {
let parameter: String

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

func hash(into hasher: inout Hasher) {
    hasher.combine(self.parameter)
}
}

Now, you can remove vashValue. It's calculated by hash(into:) automatically.