Performance question, nested for comprehensions

[ramn]

Hi, a question about performance. Reading your blogpost http://ochafik.com/blog/?p=806
you have slow code as such:

for (iteration <- 0 until iterations) {
    for (i <- 0 until n) {
    }
}

Is the performance affected if you change it to:

for (iteration <- 0 until iterations; i <- 0 until n) {
    ...
}

[ochafik]

Hi @ramn ,

Thanks for your interest :-)
These two forms are actually desugared as the exact same code:

scala.this.Predef.intWrapper(0).until(iterations).foreach[Unit](
  (iteration: Int) => scala.this.Predef.intWrapper(0).until(n).foreach[Unit](
    (i: Int) => ()
  )
)

You can check this for yourself by running scala -Xprint:typer then pasting:

val iterations = 10
val n = 20
def f1 {
  for (iteration <- 0 until iterations; i <- 0 until n) {
  }
}
def f2 {
  for (iteration <- 0 until iterations) {
    for (i <- 0 until n) {
    }
  }
}

Cheers

[ramn]

Ah interesting trick, thx