如何检查我在scala中运行时在@specialized函数或类中？

问题描述

假设我有一个专门的类和一个关联的伴侣对象：

  trait Slice [@specialized + T] {
 ... 
 
覆盖def等于（that：any）=匹配{
 case s：Slice [_] => ??? 
 case _ =>假
} 
} 
 
对象切片{
 def newInstance [@specialized T] = ??? 
 
 $ / code> 

有没有办法检查



1. 如果此实例是专用子类，则在Slice的一个方法内部
   
2. 如果另一个实例是相同的原语，
   
3. 如果我正在运行擦除或专用变体，则在伴随对象的专用方法内

而不诉诸ClassTags或手动传递Class [_]？这似乎应该是可用的信息，但我能想到的唯一方法涉及检查类的名称。

使用情况2）是特别重要的，因为我可以如果我是新手，我会将苹果与苹果进行比较，并诉诸更快的算法。它可能通过反射来完成，但是如果考虑到我们还必须处理Slice的非合成子类，那么它会非常棘手;如果我们还有

$ $ $ $ p $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $特性$ / code>

只要它们都是专用的（或两者都被擦除），应该认为它们与Slice [T]实例'兼容'？

解决方案

好吧，我想出了一个更清晰的方式：

<$ p $ （特殊字符，短，中，长，字符，浮点，双精度，布尔，任何引用）

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


private val Specializations = Seq（
解析[Byte]，
解析[Short]，
解析[Int]，
解析[Long]，
解析[Char]，
解析[
resolve [Boolean]，
resolve [Double]，
resolve [Boolean] spec => spec.key - & （特殊键[_]，ResolvedSpecialization [_]）
）.toMap.withDefaultValue（resolve [AnyRef]）

private def resolve [@specialized（AllButUnit）E：ClassTag ]：ResolvedSpecialization [E] =
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）

覆盖def等于（那：任何）=匹配{
案例r：ResolvedSpecialization [_] => r.elementType == elementType
case _ => false


override def hashCode = elementType.hashCode
}

private class SpecializedKey [@specialized（AllButUnit）E] {
重写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] .elementType 返回对应于E的特化参数的类。

Let's say I have a specialized class and an associated companion object:

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

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

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

Is there any way to check

1. Inside a method of Slice if this instance is a specialized subclass,
2. Inside a method of Slice if another instance is a specialized subclass for the same primitive,
3. Inside a specialized method on a companion object if I'm running an erased or specialized variant

without resorting to ClassTags or passing Class[_] manually? It seems like that information should be available, but the only way I can think of involves checking names of the classes.

Use case 2) is particularly important, as I could resort to faster algorithms if I new I'm comparing apples with apples. It probably could be accomplished by reflection, but it would be quite tricky when you take into account that we have to handle non-synthetic subclasses of Slice, too; if we have also

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

that should be considered 'compatible' with Slice[T] instances as long as they are both specialized (or both erased)?

解决方案

Ok, I figured out a cleaner way:

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)
}

Now specializationFor[E].elementType returns class corresponding to specialization parameter of E.

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