use English; and performance (asz)

use English; and performance

asz

created: 2006-03-02 10:53:06

perlmonks

node
author

prlmnks

node
author

hello,

i recently had to use $', so reading perlvar more carefully, i noticed it warns about using $':

The use of this variable anywhere in a program imposes a considerable performance penalty on all regular expression matches. See "BUGS".

...but in the BUGS section it states that:

Due to an unfortunate accident of Perl's implementation, use English imposes a considerable performance penalty on all regular expression matches in a program,[...]

now i'm confused :) ... i don't understand wheter use English; (i.e. $POSTMATCH) reduces performance or simply using $'.
thank you for your time!

:)))))

Re: use English; and performance

duff

created: 2006-03-02 11:04:03

perlmonks

prlmnks

Both. Read the section on performance in perldoc English

Basically, using $`, $&, and $' impose a performance penalty on all regular expression matches. Because the English module makes use of these vars, it too imposes the same performance penalty.

duff

Re^2: use English; and performance

asz

created: 2006-03-02 11:56:20

perlmonks

prlmnks

i'm trying to create a string tokenizer for a config file parser and the best that i've managed to think of is this:

#!/usr/bin/perl

use strict;
use Data::Dumper;

my $line = q[keyword1 value keyword2 "value with spaces" keyword3 value];

print Dumper tokenize_line($line);

sub tokenize_line {
    my $line = shift;

    my @tokens;
    while ($line =~ /(\S+)/g) {
        # every non-space match is a token
        push @tokens, $1;

        # anything in double-quotes is a single token
        if ($line =~ /\G\s*"(.+?)"/) {
            push @tokens, $1;
            # continue from this last match
            $line = $';
        }
    }

    return \@tokens;
}

wich outputs this:

$VAR1 = [
          'keyword1',
          'value',
          'keyword2',
          'value with spaces',
          'keyword3',
          'value'
        ];

i know it's an ugly hack, trying to substitute the original string with the rest of the matched pattern ($line = $';), but in my previous attempts i would use split and substr to achieve the same results... and it was very ugly :)
what would be a better way to write this? thank you all for your time and advice!
:)))))

Re^3: use English; and performance

Aristotle

created: 2006-03-03 11:09:55

perlmonks

prlmnks

Use /gc in your speculative match. /c prevents pos() from being reset on match failure.

Makeshifts last the longest.

Re: use English; and performance

monkey_boy

created: 2006-03-02 11:09:16

perlmonks

prlmnks

so.. to use it without the preformance issues.. straight from the docs:

use English qw(-no_match_vars);

This is not a Signature...

Re^2: use English; and performance

ikegami

created: 2006-03-02 11:15:40

perlmonks

prlmnks

The unary minus quotes identifiers, so the following is sufficient:

use English -no_match_vars;