如何在 Scala 运行时检查我在 @specialized 函数或 class 中？

Question

假设我有一个专门的 class 和一个关联的伴随对象：

trait Slice[@specialized +T] {
    ...

    override def equals(that :Any) = that match {
        case s :Slice[_] => ???
        case _ => false
    }
}

object Slice {
    def newInstance[@specialized T] = ???
}

有什么方法可以查

如果此实例是专门的子实例，则在 Slice 的方法中class，
在 Slice 的方法内，如果另一个实例是同一原语的专用子class，
如果我是运行已删除或专门的变体，则在伴随对象的专门方法中

不诉诸 Class 标签或手动传递 Class[_]？似乎该信息应该可用，但我能想到的唯一方法是检查 classes.

的名称

用例 2) 特别重要，因为如果我知道我正在比较苹果与苹果，我可以求助于更快的算法。它可能可以通过反射来完成，但是当你考虑到我们还必须处理 Slice 的非合成子 class 时，这将是非常棘手的；如果我们还有

trait ArraySlice[@specialized T] extends Slice[T] { ... }

应该考虑 'compatible' 与 Slice[T] 实例，只要它们都是专用的（或都被擦除）？

Answer 1

好的，我想出了一个更简洁的方法：

final val AllButUnit = new Specializable.Group((Byte, Short, Int, Long, Char, Float, Double, Boolean, AnyRef))

def specializationFor[@specialized(AllButUnit) E] :ResolvedSpecialization[E] =
    Specializations(new SpecializedKey[E]).asInstanceOf[ResolvedSpecialization[E]]


private val Specializations = Seq(
    resolve[Byte],
    resolve[Short],
    resolve[Int],
    resolve[Long],
    resolve[Char],
    resolve[Float],
    resolve[Double],
    resolve[Boolean],
    resolve[Unit],
    resolve[AnyRef]
).map(
    spec => spec.key -> spec :(SpecializedKey[_], ResolvedSpecialization[_])
).toMap.withDefaultValue(resolve[AnyRef])

private def resolve[@specialized(AllButUnit) E :ClassTag] :ResolvedSpecialization[E] =
    new ResolvedSpecialization[E](new SpecializedKey[E], new Array[E](0))


class ResolvedSpecialization[@specialized(AllButUnit) E] private[SpecializedCompanion]
        (val array :Array[E], val elementType :Class[E], val classTag :ClassTag[E], private[SpecializedCompanion] val key :SpecializedKey[E])
{
    private[SpecializedCompanion] def this(key :SpecializedKey[E], array :Array[E]) =
        this(array, array.getClass.getComponentType.asInstanceOf[Class[E]], ClassTag(array.getClass.getComponentType.asInstanceOf[Class[E]]), key)

    override def toString = s"@specialized($elementType)"

    override def equals(that :Any) = that match {
        case r :ResolvedSpecialization[_] => r.elementType==elementType
        case _ => false
    }

    override def hashCode = elementType.hashCode
}

private class SpecializedKey[@specialized(AllButUnit) E] {
    override def equals(that :Any) = that.getClass==getClass
    override def hashCode = getClass.hashCode

    def className = getClass.getName
    override def toString = className.substring(className.indexOf("$")+1)
}

现在specializationFor[E].elementTypereturnsclass对应E的特化参数

如何在 Scala 运行时检查我在 @specialized 函数或 class 中？

How to check I'm inside a @specialized function or class at runtime in scala?

generics

scala

type-erasure

reification