CODEWITHSUNDEEP
androidgenericskotlin
Andrei Suvorov
Andrei Suvorov

Reputation: 531

Unchecked cast at generic kotlin factory

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

Answers (1)

Wang
Wang

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

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