从类型中获取类型标签? [英] Get a TypeTag from a Type?
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问题描述
我可以使用 tpe
方法从 TypeTag[A]
获取 Type
.但是我也可以从类型中恢复类型标签吗?
I can get a Type
from a TypeTag[A]
by using the tpe
method. But can I also recover the type-tag from a type?
import scala.reflect.runtime.{universe => ru}
import ru.{Type, TypeTag}
def forward[A](implicit tt: TypeTag[A]): Type = tt.tpe
def backward(t: Type): TypeTag[_] = ???
原因是我有一个使用类型标签作为映射键的 API,但在某些时候我只有类型并删除了标签.
The reason being that I have an API that uses type-tags as keys into a map, but at some point I only have the type and dropped the tag.
推荐答案
有可能:
import scala.reflect.runtime.universe._
import scala.reflect.api
val mirror = runtimeMirror(getClass.getClassLoader) // whatever mirror you use to obtain the `Type`
def backward[T](tpe: Type): TypeTag[T] =
TypeTag(mirror, new api.TypeCreator {
def apply[U <: api.Universe with Singleton](m: api.Mirror[U]) =
if (m eq mirror) tpe.asInstanceOf[U # Type]
else throw new IllegalArgumentException(s"Type tag defined in $mirror cannot be migrated to other mirrors.")
})
assert(backward[String](forward[String]) == typeTag[String])
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