Verwendung von scalar (@list) in Schleifen wenn Listenlänge konstant ist? - #184735 (Allgemeines zu Perl)

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2016-05-17 15:37

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2005-06-01
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Mit scalar innerhab jeder Schleifeniteration wird's langsamer.

Code (perl): (dl )

use warnings;
use strict;
use Benchmark "timethese";

my $count = 5000;
my @array = qw( a b c );
my $glbArraySize = scalar( @array );

timethese(
    10000,
    {
        "scalarSavedGlobally"    => sub {
            for ( 1 .. $count ) {
                my $foo = 1 if $glbArraySize == $_;
            }
        },
        "scalarSavedLocally"    => sub {
            my $arraySize = scalar( @array );
            for ( 1 .. $count ) {
                my $foo = 1 if $arraySize == $_;
            }
        },
        "scalarNotSaved" => sub {
            for ( 1 .. $count ) {
                my $foo = 1 if scalar( @array ) == $_;
            }
        }
    }
);

Ausgabe:

Code: (dl )

Benchmark: timing 10000 iterations of scalarNotSaved, scalarSavedGlobally, scalarSavedLocally...
scalarNotSaved:  9 wallclock secs ( 9.14 usr +  0.00 sys =  9.14 CPU) @ 1093.85/s (n=10000)
scalarSavedGlobally:  6 wallclock secs ( 5.63 usr +  0.00 sys =  5.63 CPU) @ 1775.57/s (n=10000)
scalarSavedLocally:  6 wallclock secs ( 5.68 usr +  0.00 sys =  5.68 CPU) @ 1761.18/s (n=10000)

Everyone knows that debugging is twice as hard as writing a program in the first place. So if you're as clever as you can be when you write it, how will you ever debug it? -- Brian Kernighan: "The Elements of Programming Style"