如何在Scala中将嵌套泛型类型用作方法返回类型

Question

I have a few methods that would like to use a nested generic type as its return type.

import scala.language.higherKinds

trait DBClient {
  def execute[T[U] <: DataStoreItem[U]](ops: ScanamoOps[Result[T]]): Future[U]
}

But this doesn't work. I am not able to use U in my return Type. Is there any other way to define a method like the one above where I can use a nested type U in my return type.

I also Tried:

trait DBClient {
  def execute[U, T <: DataStoreItem[U]](ops: ScanamoOps[Result[T]]): Future[U]
}

Which doesn't work either. Thanks for helping, I am very new to scala generics and higher order types. So please excuse my ignorance.

Answer 1

I got it almost right.

import scala.language.higherKinds

trait DBClient {
  def execute[T[U0] <: DataStoreItem[U0], U](ops: ScanamoOps[Result[T[U]]]): Future[U]
}