structural types are slow :-)

structural_types_slow.scala

package com.typesafe.benchmarks

import java.util.concurrent.TimeUnit

import org.openjdk.jmh.annotations._

@State(Scope.Benchmark)
@BenchmarkMode(Array(Mode.AverageTime))
@OutputTimeUnit(TimeUnit.NANOSECONDS)
class ReflectBenchmark {

  trait Cache {
    def cache(a: AnyRef): AnyRef
  }

  class RealCache extends Cache {
    def cache(a: AnyRef): AnyRef = a
  }
  class RealCache2 extends Cache {
    def cache(a: AnyRef): AnyRef = a
  }
  class RealCache3 extends Cache {
    def cache(a: AnyRef): AnyRef = a
  }

  type StructuralCache = {
    def cache(a: AnyRef): AnyRef
  }

  val realCache = new RealCache
  val realCache2 = new RealCache2
  val realCache3 = new RealCache3

  val cache: Cache = new RealCache

  val structuralCache: StructuralCache = new RealCache

  @Benchmark def direct = realCache.cache("")
  @Benchmark def iface = cache.cache("")
  @Benchmark def struct = structuralCache.cache("")

  /*
    Benchmark                Mode  Cnt   Score   Error  Units
    ReflectBenchmark.direct  avgt   40   3.355 ± 0.184  ns/op
    ReflectBenchmark.iface   avgt   40   3.394 ± 0.090  ns/op
    ReflectBenchmark.struct  avgt   40  10.277 ± 0.894  ns/op
   */
}

Just out of curiosity... Is this @Benchmark that you're using a wrapped ScalaMeter library utility underneath or some secret Typesafe's sauce for microbenchmarking (not available in public)?