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Swift Generic Downcast Question
protocol BaseProtocol {
func doIt()
protocol DerivedProtocol : BaseProtocol {
func hello()
class MyObject: DerivedProtocol {
func doIt() { print("doIt") }
func hello() { print("hello") }
let o = MyObject()
// BTW: I do not want `func workOnDerived(value: DerivedProtocol)` here,
// this is supposed to receive the full type `T` from workOnBase.
func workOnDerived<T: DerivedProtocol>(value: T) {
func workOnBase<T: BaseProtocol>(value: T) {
// the compiler still has the full type T here,
// i.e. T is `MyObject`
if value is DerivedProtocol {
// how can I call workOnDerived(value)?
// or in other words, how to I downcast the protocol
// requirement?
workOnDerived(value: value) // how??
else { fatalError("unexpected") }
workOnBase(value: o) // entry point, cannot control this
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