Generic interface to service that can return many different types

ValueMaker.swift

//I am some 3P service. I can be asked for many different types of values.
class ValueMaker {
    static func makeBool() -> Bool { return true }
    static func makeInt() -> Int { return 3 }
}

//I am a 1P abstraction over that service. 
//  I want to save effort in the rest of my codebase by exposing 1 func for getting values, 
//  instead of needing a different func for each possible type our 3P service can vend. So I use a func with a generic return type.
func genericMaker<T: TypeEmittedByOur3PService>() -> T? {

    //I switch on T.self because my behavior needs to vary with T
    switch T.self {
    case is Bool.Type:
        return ValueMaker.makeBool() as? T
    case is Int.Type:
        return ValueMaker.makeInt() as? T
    default:
        return nil
    }
}

//Then, because we constrained T in the func genericMaker definition, we can add protocol conformance to various types
//  to tell Xcode what values we're allowed to ask our 1P abstraction for.
protocol TypeEmittedByOur3PService { }
extension Bool: TypeEmittedByOur3PService { }
extension Int: TypeEmittedByOur3PService { }

//genericMaker knows which T to use merely by the explicit type declared on these initializations
let goodBool: Bool? = genericMaker()
let goodInt: Int? =  genericMaker()