Why can't I check at runtime if `Listener<T>...
# announcementsz
ziggy42
03/19/2018, 2:40 PMWhy can't I check at runtime if
Listener<T>Listener<User>d
diesieben07
03/19/2018, 2:41 PMz
ziggy42
03/19/2018, 2:41 PMSo there's no way to check for this?
k
karelpeeters
03/19/2018, 2:42 PMMaybe you can hack something together using reified functions, depends on your use case.
z
ziggy42
03/19/2018, 2:46 PMfun <T> subscribe(topic: Topic, listener: Listener<T>)d
diesieben07
03/19/2018, 2:47 PMYou can make the function
inlinereifiedT::classz
ziggy42
03/19/2018, 2:47 PMFor each topic there's a specific T that is acceptable
a
Andreas Sinz
03/19/2018, 2:47 PMif its the use-case from earlier, there is no way to do that without unsafe casts
d
diesieben07
03/19/2018, 2:48 PMIn that case
Topic<T>a
Andreas Sinz
03/19/2018, 2:48 PMand to compare types you need to use
KClassz
ziggy42
03/19/2018, 2:48 PMYes, same, I was searching for the least ugly way to do this
a
Andreas Sinz
03/19/2018, 2:49 PMbecause of type erasure there is no safe way to do that unfortunately
z
ziggy42
03/19/2018, 2:51 PM😕
d
diesieben07
03/19/2018, 2:52 PMIf
Topicz
ziggy42
03/19/2018, 2:52 PMBut
Topicenumd
diesieben07
03/19/2018, 2:52 PMMaybe it should be a
sealed classz
ziggy42
03/19/2018, 3:02 PM Copy code
@Suppress("unused")
sealed class TopicWrapper<T>
class UserTopicWrapper : TopicWrapper<User>() {
companion object {
val INSTANCE = UserTopicWrapper()
}
} Copy code
fun <T> subscribe(topic: TopicWrapper<T>, listener: Listener<T>) {
when (topic) {
is UserTopicWrapper -> {
@Suppress("UNCHECKED_CAST")
userListeners.add(listener as Listener<User>)
}
}
}d
diesieben07
03/19/2018, 3:03 PMWhy not
object UserTopicWrapper : TopicWrapper<User>()z
ziggy42
03/19/2018, 3:04 PMVery cool 😄
ziggy42
03/19/2018, 3:04 PMSome other edits?
d
diesieben07
03/19/2018, 3:05 PMYou could out-source the adding to the
Topicdiesieben07
03/19/2018, 3:05 PMBut other than that, looks alright
z
ziggy42
03/19/2018, 3:07 PMMm so you'd move the listeners to
TopicWrapperziggy42
03/19/2018, 3:08 PMYeah you avoid the unchecked cast but then everybody can touch the listeners variable right?
d
diesieben07
03/19/2018, 3:09 PMNo, not really. I am not 100% sure of your setup, but something like this:
Copy code
sealed class TopicWrapper<T> {
abstract fun addListener(listener: Listener<T>, userListeners: MutableList<Listener<User>>, otherListeners: MutableList<Listener<Other>>
}diesieben07
03/19/2018, 3:10 PMLike so:
Copy code
object UserTopic : TopicWrapper<User> {
override fun addListener(listener: Listener<User>, userListeners: MutableList<Listener<User>>, otherListeners: MutableList<Listener<Other>> {
userListeners += listener
}diesieben07
03/19/2018, 3:10 PMNo unchecked cast anywhere 😉
a
Andreas Sinz
03/19/2018, 3:11 PMand then he ends up with a property per type which he tried to avoid ^^
d
diesieben07
03/19/2018, 3:11 PMThat suggests otherwise...userListeners.add(listener as Listener<User>)
z
ziggy42
03/19/2018, 3:12 PMIf I do it like this I can just create N functions for N types
ziggy42
03/19/2018, 3:13 PMWhich I will do because I've lost enough time on this for today 😄
a
Andreas Sinz
03/19/2018, 3:13 PMd
diesieben07
03/19/2018, 3:13 PMAh, yes okay. Then there is no way to avoid the unchecked cast. Sorry 🙈
a
Andreas Sinz
03/19/2018, 3:14 PM@ziggy42 what is more important to you? having one list per type or using an unchecked cast?
z
ziggy42
03/19/2018, 3:15 PMI'd prefer to avoid the unchecked cast
2 Views