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in reply to Re^7: What esteemed monks think about changes necessary/desirable in Perl 7 outside of OO staff
in thread What esteemed monks think about changes necessary/desirable in Perl 7 outside of OO staff

No elegant alternative. As I showed in the benchmark, this works fine: 

sub splt{split" ",reverse((split" ",(reverse$x),1)[0]),1;};

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The most elegant approach to this problem is the use of tr function. The implementation below beats regex three times and can be made faster by trivial extension of tr function mentioned in my prev post (something like option 'x' -- stop the translation on the first symbol outside the set1 and return this position), which can be used instead of more general function index for searching single characters in the string and can made like rindex to be able to search in reverse direction too.

Looks like the solution for trim from the Cookbook mentioned by Fletch along with potentially deforming the string is slower then regex in my test(on my machine it took 3.56 sec real time).

Here is the "tr based" algorithm for trim: 

time perl -e 'for (1..1000000) { $line=" aaa bbb ccc ddd eee fff "; $_=$line; $_=~tr/ /x/c; $start=index($_,'x'); $line=substr($line,$start,rindex($_,'x')-$start+1); }'

real 0m1.112s
user 0m1.076s
sys 0m0.031s
Can be made into a single statement making it slightly( ~7%) slower: 
$line=substr($line,($start=index($_=$line=~tr/ /x/cr,'x')),rindex($_,'x')-$start+1);

# time perl -e 'for (1..1000000) { $line=" aaa bbb ccc ddd eee fff "; $line=substr($line,($start=index($_=$line=~tr/ /x/cr,'x')),rindex($_,'x')-$start+1); }' 
real 0m1.189s
user 0m1.154s
sys 0m0.015s
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Re^9: What esteemed monks think about changes necessary/desirable in Perl 7 outside of OO staff
by likbez (Sexton) on Sep 16, 2020 at 13:45 UTC
    or 
    $line=substr($line,index($_=$line=~tr/ /x/cr,'x')),rindex($_,'x')-leng
+th($line)+1);

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      So, restricting to solutions that do not compress internal spaces, and ignoring the fact that " " is identical to \s, I am surprised that split is faster than tr. Converted the one-liner to a script for readability):

      $ cat test.pl
use 5.18.0;
use warnings;

use Benchmark qw( cmpthese );

my $x = join "    " => "", ("abc") x 5, "";

sub splt {
    split " ", reverse ((split " ", (reverse $x), 1)[0]), 1;
    }
sub rgx {
    $x =~ s/^\s+//r =~ s/\s+$//r;
    }
sub trx {
    my $y = $x =~ y/ /x/cr;
    substr ($x, index ($y, "x"), rindex ($y, "x") - length ($x) + 1);
    }

say "sourc: |$x|";
say "split: |", splt (), "|";
say "regex: |", rgx  (), "|";
say "tr/x/: |", trx  (), "|";

cmpthese (-2, { splt => \&splt, rgx => \&rgx, trx => \&trx });

      [download]
      $ perl test.pl
sourc: |    abc    abc    abc    abc    abc    |
split: |abc    abc    abc    abc    abc|
regex: |abc    abc    abc    abc    abc|
tr/x/: |abc    abc    abc    abc    abc|
          Rate  rgx  trx splt
rgx  1047602/s   -- -59% -65%
trx  2553722/s 144%   -- -14%
splt 2958598/s 182%  16%   --

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      So far, none of the presented alternatives to s{^\s+}{}r and friends appeal to me, even though twice as fast or more, I would definitely choose the regex one over the magic of the other two. YMMV.

      Here's the one that also squeezes internal spaces with no \s, and there I would seriously consider the join/split variant:

      $ cat test.pl
use 5.18.0;
use warnings;

use Benchmark qw( cmpthese );

my $x = join "    " => "", ("abc") x 5, "";

sub splt {
    join " " => split " " => $x;
    }
sub rgx {
    $x =~ tr/ / /sr =~ s/^ //r =~ s/ $//r;
    }
sub trx {
    my $y = $x =~ tr/ /x/cr;
    substr ($x, index ($y, "x"), rindex ($y, "x") - length ($x) + 1) =
+~ tr/ / /sr;
    }

say "sourc: |$x|";
say "split: |", splt (), "|";
say "regex: |", rgx  (), "|";
say "tr/x/: |", trx  (), "|";

cmpthese (-2, { splt => \&splt, rgx => \&rgx, trx => \&trx });

      [download]
      $ perl test.pl
sourc: |    abc    abc    abc    abc    abc    |
split: |abc abc abc abc abc|
regex: |abc abc abc abc abc|
tr/x/: |abc abc abc abc abc|
          Rate  rgx splt  trx
rgx  1012851/s   -- -42% -52%
splt 1739341/s  72%   -- -17%
trx  2105282/s 108%  21%   --

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      Enjoy, Have FUN! H.Merijn
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[d/l]
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      You probably meant 
      substr($x, index($_ = $x =~ tr/ /x/cr, 'x'), rindex($_, 'x') - length(
+$x) + 1)

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      map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
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        Does not matter what variable you use: 

        # perl -e ' { $line="   aaa bbb ccc ddd eee fff    ";  $line=substr($l
+ine,index($_=$line=~tr/ /x/cr,'x'),rindex($_,'x')-length($line)+1); p
+rint qq(|$line|\n)}'
|aaa bbb ccc ddd eee fff|

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