Reputation: 531
I'm trying to make a generic factory in kotlin for parsing some string into Model classes:
internal interface Model
data class UserId(val id: String, val name: String, val link: String): Model
data class Shelf(val id: String, val name: String, val bookCount: Int): Model
internal inline fun <reified T: Model> getParser(): Parser<T> {
return when (T::class) {
UserId::class -> UserIdParser() as Parser<T>
Shelf::class -> UserShelvesParser() as Parser<T>
else -> throw Exception("can't match proper parser")
}
}
internal interface Parser<out T: Model> {
fun parse(xml: String): T
}
internal class UserIdParser : Parser<UserId> {
override fun parse(xml: String): UserId {
return parseUserId(xml)
}
}
internal class UserShelvesParser : Parser<Shelf> {
override fun parse(xml: String): Shelf {
return parseShelf(xml)
}
}
// for example
internal fun parseUserId(xml: String) = UserId("123", "owl", "ya.ru")
internal fun parseShelf(xml: String) = Shelf("123", "to-read", 20)
So in client code, I could write this:
val t = getParser<UserId>().parse("")
It works, but at getParser
method I've got warning Unchecked cast from UserIdParser to Parser<T>
. How could I achieve such behavior in kotlin, without the warnings in idiomatic way?
Upvotes: 1
Views: 2105
Reputation: 1038
This is slightly different from what you are aiming for, but it works without any warning:
internal interface Model
data class UserId(val id: String, val name: String, val link: String) : Model
data class Shelf(val id: String, val name: String, val bookCount: Int) : Model
internal inline fun <reified T : Model> parse(xml: String) = when (T::class) {
UserId::class -> parseUserId(xml)
Shelf::class -> parseShelf(xml)
else -> throw Exception("can't match proper parser")
} as T
// for example
internal fun parseUserId(xml: String) = UserId("123", "owl", "ya.ru")
internal fun parseShelf(xml: String) = Shelf("123", "to-read", 20)
then it can be called like that:
val t = parse<UserId>("")
Hope this can help you.
Upvotes: 5