我有一段代码，概念上类似于以下代码：
//library code
trait Support[K,V]
def partialHandler[K,V](key: K,value: V)(implicit ev: Support[K,V]) = ???
//user code
implicit val intIntSupport = new Support[Int,Int] {}
implicit val intStringSupport = new Support[Int,String] {}
...
partialHandler(1,"foo)
partialHandler(1,1)
我想知道是否有一种方法可以让该库的用户更优雅地定义受支持的(K,V)类型，例如：
val supportedTypes = new Support[Int,Int] {} :: new Support[Int,String] {} :: HNil
（本质上，我正在寻找从几乎未知的HList到Support[K,V]的隐式转换。这看起来不可行，但也许我遗漏了某些东西。）
尝试隐式supportedTypes
import shapeless.ops.hlist.Selector
import shapeless.{HList,HNil}
// library code
trait Support[K,V]
object Support {
implicit def mkSupport[L <: HList,K,V](implicit l: L,sel: Selector[L,Support[K,V]]): Support[K,V] = null
}
def partialHandler[K,V](key: K,value: V)(implicit ev: Support[K,V]) = ???
//user code
implicit val supportedTypes = new Support[Int,Int] {} :: new Support[Int,String] {} :: new Support[Long,Double] {} :: HNil
partialHandler(1,"foo")
partialHandler(1,1)
partialHandler(1L,1.0)
// partialHandler("foo","bar") // doesn't compile