Re^3: counting backward

[BrowserUk]

in reply to Re^2: counting backward
in thread counting backward

You caught that I use 1; as the body of the loop to avoid confusing things with the efficiency of the system null device driver (not particularly efficient on Win32). But you missed the point I was trying to make; namely that you cannot use the C-style for as a modifier; which means you must always pay the penalty of creating a new scope for each iteration of the loop.

Add that to the benchmark to see that cost:

#! perl
use strict;
use warnings;
#use IO::Null;
use Benchmark qw( cmpthese );

my $n = 1e4;
#my $null = IO::Null->new;
cmpthese 10000, {
    foreach_loop => \&foreach_loop,
    foreach_modifier => \&foreach_modifier,
    c_for_loop   => \&c_for_loop,
};

sub foreach_loop {
    for my $i (-$n .. 0) {
        # $null->print( -$i );
        1;
    }
}

sub foreach_modifier {
    1 for -$n .. 0;
}

sub c_for_loop {
    for (my $j = $n; $j >= 0; --$j) {
        # $null->print( $j );
        1;
    }
}

__END__
C:\test>junk
                   Rate       c_for_loop     foreach_loop foreach_modi
+fier
c_for_loop        922/s               --             -41%             
+-52%
foreach_loop     1573/s              71%               --             
+-18%
foreach_modifier 1922/s             108%              22%             
+  --

Of course, some people eschew the use of modifier forms; but then they are probably the same people that favor their own one-off developer time over the every-user, every-time runtime costs.

As for much of my work I am both user and developer, I don't have that luxury.