Scala string concatenation benchmark

out.txt

[info] Benchmark                                              Mode  Cnt         Score         Error  Units
[info] StringConcatenationBenchmark.stringBuilder            thrpt   20  24401716.742 ±  759067.927  ops/s
[info] StringConcatenationBenchmark.stringBuilderViaVarargs  thrpt   20  11990758.447 ±  942632.452  ops/s
[info] StringConcatenationBenchmark.stringConcat             thrpt   20  30990302.536 ± 2168504.239  ops/s
[info] StringConcatenationBenchmark.stringConcatFn           thrpt   20  31361529.780 ± 2022207.795  ops/s
[info] StringConcatenationBenchmark.stringConcatVarArgs      thrpt   20   7348008.964 ±  234634.594  ops/s
[info] StringConcatenationBenchmark.stringConcatVarArgs2     thrpt   20   5662366.576 ±  115998.273  ops/s
[info] StringConcatenationBenchmark.stringContext            thrpt   20   7612447.788 ±  451671.634  ops/s
[info] StringConcatenationBenchmark.stringFormat             thrpt   20    901011.458 ±   22039.147  ops/s
[info] StringConcatenationBenchmark.stringMkString           thrpt   20   4748503.980 ±   85292.496  ops/s

StringConcatenationBenchmark.scala

import java.util.concurrent.TimeUnit
import org.openjdk.jmh.annotations._

/**
 * The following command will run the benchmarks with reasonable settings:
 *
 * > sbt "benchmark/jmh:run -i 10 -wi 10 -f 2 -t 1 StringConcatenationBenchmark"
 */
@State(Scope.Thread)
@BenchmarkMode(Array(Mode.Throughput))
@OutputTimeUnit(TimeUnit.SECONDS)
class StringConcatenationBenchmark {

  def times(s: String)(i: Int) = s
  def text = "asdf"

  @Benchmark
  def stringFormat = String.format("%s%s%s", times("a")(42), text, times("c")(43))

  @Benchmark
  def stringContext = s"${times("a")(42)}$text${times("c")(43)}"

  @Benchmark
  def stringConcat: String = times("a")(42).concat(text).concat(times("c")(43))

  @Benchmark
  def stringConcatFn: String = stringConcatter(times("a")(42), text, times("c")(43))

  @inline def stringConcatter(a: String, b: String, c: String) = {
    a.concat(b).concat(c)
  }

  @Benchmark
  def stringConcatVarArgs: String = stringConcatVarargs(times("a")(42), text, times("c")(43))

  @inline def stringConcatVarargs(ss: String*) = {
    ss.fold("") { case (l, r) => l.concat(r) }
  }

  @Benchmark
  def stringConcatVarArgs2: String = stringConcatVarargs2(times("a")(42), text, times("c")(43))

  @inline def stringConcatVarargs2(ss: String*) = {
    var s = ss.head
    for (x <- ss.tail)
      s = s.concat(x)
    s
  }

  @Benchmark
  def stringMkString: String = Seq(times("a")(42), text, times("c")(43)).mkString

  @Benchmark
  def stringBuilder: String = new StringBuilder(times("a")(42)).append(text).append(times("c")(43)).toString

  @Benchmark
  def stringBuilderViaVarargs: String = stringBuilderFromVarargs(times("a")(42), text, times("c")(43))

  def stringBuilderFromVarargs(ss: String*) = {
    val sb = new StringBuilder
    ss.foreach(s => sb.append(s))
    sb.toString
  }
}