Say I want a type variable, T, that extends a certain class and implements an interface. Something like:
class Foo <T : Bar implements Baz> { ... } What is the syntax for this in Kotlin?
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1 Answer
Only one upper bound can be specified inside the angle brackets.
Kotlin offers different syntax for generic constraints when there is more than one constraint:
class Foo<T>(val t: T) where T : Bar, T : Baz { ... } and for functions:
fun <T> f(): Foo where T : Bar, T : Baz { ... } It is documented here.
3 Comments
Ufkoku
Is there any way to use it for parametr type of fun, for example, fun foo(arg : ClassType, InterfaceType){}? Without adding type parameter to class
hotkey
@Ufkoku, no, there's no way to do it: there's no intersection types in Kotlin, and generic parameters can only be declared explicitly.
leimenghao
@hotkey I have a function below:
fun <T> wrapClientListener(listener: RemoteController.OnClientUpdateListener): T where T : RemoteController.OnClientUpdateListener, T : NotificationListenerService. I don't care of T's type. But When I call this method, Kotlin asks for the specific type. So how can i call this method?