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Re^2: I need perl coding standards

by siracusa (Friar)
on May 29, 2005 at 00:47 UTC ( #461433=note: print w/replies, xml ) Need Help??

in reply to Re: I need perl coding standards
in thread I need perl coding standards

I found this bit odd:
Do not use shift. Use @_. shift is slower, and Brian has an allergic reaction to it.
my $var = shift; # wrong my($var) = @_; # right sub foo { uc $_[0] } # OK my($var1, $var2) = (shift, shift); # Um, no.
I always use shift, and I recall benchmarking it way back in the day before I made that decision, just to make sure it wasn't slower. Here's the test I used, and the results:
use Benchmark qw(cmpthese); sub x_shift { while(@_) { my $a = shift; } } sub x_copy1 { for(my $i = 0; $i < $#_; $i++) { my $a = $_[$i]; } } sub x_copy2 { my $end = $#_; for(my $i = 0; $i < $end; $i++) { my $a = $_[$i]; } } my @args = (1 .. 100); cmpthese(1000000, { x_shift => 'x_shift(@args)', x_copy1 => 'x_copy1(@args)', x_copy2 => 'x_copy2(@args)' });
Rate x_copy2 x_copy1 x_shift x_copy2 609756/s -- -18% -45% x_copy1 746269/s 22% -- -32% x_shift 1098901/s 80% 47% --
Seeing the flat claim that shift is slower made me rethink my earlier test and try something more simple:
use Benchmark qw(cmpthese); sub x_shift { my $a = shift } sub x_copy { my $a = $_[0] } my @args = (1 .. 3); cmpthese(1000000, { x_shift => 'x_shift(@args)', x_copy => 'x_copy(@ar +gs)' });
Sure enough, the results changed, but now it appears to be a tie:
Rate x_copy x_shift x_copy 1298701/s -- -0% x_shift 1298701/s 0% --

The results fluctuate a few percent in each direction. Anyway, my point is that I don't think performance is a reason to avoid using shift.

(I have a whole directory of benchmarks for silly little things, e.g. benchmarking exists() vs. a test for truth on a hash key and crazy stuff like that. It's a disease...but it amuses me :-)

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