::: generally better for List[A]

gistfile1.scala

➜  scala-2.10.1    bin/scala -cp "/Users/ryan/dev/research/thyme/Thyme.jar"
Welcome to Scala version 2.10.1 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_45).
Type in expressions to have them evaluated.
Type :help for more information.

scala> val th = new ichi.bench.Thyme
th: ichi.bench.Thyme = ichi.bench.Thyme@786f9982

scala> val l1 = List.range(1,1000)

scala> val l2 = List.range(1,1000)

scala> th.pbench { l1 ++ l2 }
Benchmark (81900 calls in 2.200 s)
  Time:    25.13 us   95% CI 24.08 us - 26.18 us   (n=20)
  Garbage: 293.0 ns   (n=14 sweeps measured)

scala> th.pbench { l1 ::: l2 }
Benchmark (81900 calls in 2.150 s)
  Time:    25.25 us   95% CI 24.15 us - 26.35 us   (n=20)
  Garbage: 244.1 ns   (n=11 sweeps measured)

scala> th.pbench { l1 ::: Nil }
Benchmark (671088620 calls in 2.529 s)
  Time:    3.755 ns   95% CI 3.624 ns - 3.886 ns   (n=20)

scala> th.pbench { l1 ++ Nil }
Benchmark (83886060 calls in 1.593 s)
  Time:    17.71 ns   95% CI 16.68 ns - 18.75 ns   (n=20)
  Garbage: 0.3338 ns   (n=16 sweeps measured)

scala> 671088620 > 83886060
res4: Boolean = true