in reply to RE: Buzzcutbuddha(You provided disinformation): C Style For and Foreach The Same
in thread Finding the length of an array of arrays

Read what I wrote exactly as I wrote it the first time.

I said that foreach loops are faster than classic C-style loops. Yes, you can write a classic C-style loop using foreach. But nobody thinks that way.

And indeed iterating directly over a list is *significantly* faster, less error prone, etc, than doing an explicit loop over the indices, looking up array values inside the loop. That is not disinformation, that is simple fact and I have found that that factual information carries a lot more weight with C programmers starting out with Perl than saying, "Well the standard Perl idiom is..."

Have you ever said, "This is Perl Style and easier to understand." and been told, "Well I am a C programmer, I have been using for loops for 15 years and they are easier for me to understand because I am used to them."? You won't win that argument...

  • Comment on RE: RE: Buzzcutbuddha(You provided disinformation): C Style For and Foreach The Same

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RE: Buzzcutbuddha(I Stand Corrected): C Style For and Foreach The Same
by buzzcutbuddha (Chaplain) on Aug 19, 2000 at 00:34 UTC
    I stand corrected. You are correct on your points. Sorry for the accusation. For those interested, here is the code and results from benchmarking.
    code: 
    use Benchmark;

sub foreach1000()
{
    my @x = (1..1000);
    foreach(@x)
    {
        my $z = $_;
    }
}

sub for1000()
{
    my @x = (1..1000);
    for(my $y = 0; $y < scalar(@x); $y++)
    {
        my $z = $x[$y];
    }
}

sub foreach10000()
{
    my @x = (1..10000);
    foreach(@x)
    {
        my $z = $_;
    }
}

sub for10000()
{
    my @x = (1..10000);
    for(my $y = 0; $y < scalar(@x); $y++)
    {
        my $z = $x[$y];
    }
}

timethese( 10000, { for1000 => 'for1000()', foreach1000 => 'foreach100
+0()', for10000 => 'for10000()', foreach10000 => 'foreach10000()' });

    [download]
    results: 
    Benchmark: timing 10000 iterations of for1000, for10000, foreach1000, 
+foreach10000...
   for1000: 59 wallclock secs (53.75 usr +  0.03 sys = 53.78 CPU) @ 18
+5.95/s (n=10000)
  for10000: 676 wallclock secs (537.40 usr +  0.23 sys = 537.63 CPU) @
+ 18.60/s (n=10000)
foreach1000: 33 wallclock secs (24.67 usr +  0.00 sys = 24.67 CPU) @ 4
+05.27/s (n=10000)
foreach10000: 293 wallclock secs (250.74 usr +  0.21 sys = 250.95 CPU)
+ @ 39.85/s (n=10000)

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      I re-ran these benchmarks with a minor optimization on the 'scalar(@x)' portion of the loop. It basically proved that the compiler isn't performing an optimization on the limit term in the loop. I'm a little surprised that since the array isn't being modified, and no functions are being called, the compiler didn't optimize that out to a fixed value. Of course, I'm speaking as an old 'C' coder... 
      Benchmark: timing 10000 iterations of for1000, for10000, for10000a, fo
+r1000a, foreach1000, foreach10000...
   for1000: 73 wallclock secs (60.06 usr +  0.16 sys = 60.22 CPU)
  for10000: 795 wallclock secs (632.63 usr +  1.39 sys = 634.02 CPU)
 for10000a: 508 wallclock secs (398.29 usr +  0.89 sys = 399.18 CPU)
  for1000a: 45 wallclock secs (37.13 usr +  0.06 sys = 37.19 CPU)
foreach1000: 30 wallclock secs (24.32 usr +  0.06 sys = 24.38 CPU)
foreach10000: 360 wallclock secs (276.53 usr +  0.69 sys = 277.22 CPU)

use Benchmark;

sub foreach1000()
{
    my @x = (1..1000);
    foreach(@x)
    {
        my $z = $_;
    }
}

sub for1000()
{
    my @x = (1..1000);
    for(my $y = 0; $y < scalar(@x); $y++)
    {
        my $z = $x[$y];
    }
}

sub for1000a()
{
    my @x = (1..1000);
    my $len = scalar(@x);
    for(my $y = 0; $y < $len; $y++)
    {
        my $z = $x[$y];
    }
}

sub foreach10000()
{
    my @x = (1..10000);
    foreach(@x)
    {
        my $z = $_;
    }
}

sub for10000()
{
    my @x = (1..10000);
    for(my $y = 0; $y < scalar(@x); $y++)
    {
        my $z = $x[$y];
    }
}

sub for10000a()
{
    my @x = (1..10000);
    my $len = scalar(@x);
    for(my $y = 0; $y < $len; $y++)
    {
        my $z = $x[$y];
    }
}

timethese( 10000, { for1000 => 'for1000()', 
            for1000a => 'for1000a()',
            foreach1000 => 'foreach1000()', 
            for10000 => 'for10000()', 
            for10000a => 'for10000a()',
            foreach10000 => 'foreach10000()' });

      [download]


      --Chris

      e-mail jcwren
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