Scala 中的方法调用反射会导致性能下降吗？

Question

I have a method intended to do some simple statistics for data IO, as shown below.

def ioStatSink[T <: { def length: Int }](): Sink[T, Future[(Long, Long)]] = Sink.fold((0L, 0L))((acc, bytes) => (acc._1 + 1L, acc._2 + bytes.length))

As I want it to be able to handle different data types that have a { def length: Int } method, I make it generic.
The problem is, this method invocation uses reflection.
As this method is called millions fo times, I don't want it to have performance issue.
I know class instantiation with reflection has performance penalty, but how about this method invocation?

(another issue about the method is, it cannot adapt to types with a method of { def length: Long } , any suggestion to deal with this?)

Answer 1

Since you said you were interested in the typeclass alternative.
Here is a simple demo.

import scala.language.higherKinds

trait Sizeable[T] {
  def size(t: T): Long
}

object Sizeable {
  private final val _IterableOnceSizable: Sizeable[IterableOnce[_]] =
    new Sizeable[IterableOnce[_]] {
      override final def size(iter: IterableOnce[_]): Long = {
        val knownSize = iter.knownSize
        if (knownSize == -1) iter.iterator.size.toLong
        else knownSize.toLong
      }
    }

  implicit final def CollectionSizeable[C[_], T](implicit ev: C[T] <:< IterableOnce[T]): Sizeable[C[T]] =
    _IterableOnceSizable.asInstanceOf[Sizeable[C[T]]]
}

object syntax {
  object sizeable {
    implicit class SizeableOps[T](private val sizable: T) extends AnyVal {
      @inline def size(implicit ev: Sizeable[T]): Long =
        ev.size(sizable)

      @inline def length(implicit ev: Sizeable[T]): Long =
        ev.size(sizable)
    }
  }
}

import syntax.sizeable._

def ioStatSink[T : Sizeable](): Sink[T, Future[(Long, Long)]] =
  Sink.fold((0L, 0L))((acc, bytes) => (acc._1 + 1L, acc._2 + bytes.length))