在Kotlin中，如何使用本机Java参数实例化泛型类？

Question

I am exploring using BDB JE (Berkeley DB Java Edition) with Kotlin. Knowledge of BDB is not necessary to answer this question.

BDB has a method that looks like this:

store.getPrimaryIndex(Int::class.java, "Int", Person::class.java, "Person")

I want to do things generically, so I wrote this

inline fun <reified TModel : Any, reified TKey : Any> getIndex() = 
    return store.getPrimaryIndex(TKey::class.java, TKey::class.simpleName, TModel::class.java, Model::class.simpleName)

So far so good. I now want to pass this index object to a class, which looks like this:

class ModelStore<TModel, TKey>(index : PrimaryIndex<TKey, TModel>) {
    private val index = index

    fun get(key : TKey): TModel = index.get(key)
    fun put(model : TModel) = index.put(model)
}

But if I try and pass the output from getIndex<User, Int>() to ModelStore<User, Int> I get the following error:

Type inference failed: Expected type mismatch: Inferred type is PrimaryIndex<TModel!, TKey!>! but PrimaryIndex<TModel, TKey> was expected.

My question: Can I pass the the index to the ModelStore ? How do I convince the type-system that this is kosher?

Answer 1

The simplest workaround is to cast the types:

ModelStore<User, Int>(getIndex<User, Int>() as PrimaryIndex<User, Int>)

Also I would expect it to work without specifying the types:

ModelStore(getIndex<User, Int>())