in reply to Collapsing repetitive equality tests: || vs {} vs // (an observation)

if (/^(A|B|C)$/) { }
should be
if (/^(A|B|C)\z/) { }
to be equivalent.

And
if (/^(A|B|C)\z/) { }
would be faster if the needless capture was removed.
if (/^(?:A|B|C)\z/) { }

By the way, I don't trust "Benchmarking says ..." without seeing the test. They're too easy to do wrong. In fact, my benchmarks disagree with your findings.

Findings:

Summary results: 

if:    ($var eq "A" || $var eq 'B' || $var eq 'C')
ihash: { A=>1, B=>1, C=>1 }->{$var}
shash: $hash{$var}
re:    $var =~ /^(?:A|B|C)\z/

Benchmarking no matches

           Rate ihash    re    if shash
ihash  328339/s    --  -79%  -81%  -86%
re    1557274/s  374%    --  -10%  -33%
if    1738308/s  429%   12%    --  -25%
shash 2307394/s  603%   48%   33%    --

Benchmarking match A

           Rate ihash    re shash    if
ihash  333900/s    --  -78%  -83%  -88%
re    1532032/s  359%    --  -21%  -43%
shash 1946689/s  483%   27%    --  -28%
if    2707780/s  711%   77%   39%    --

Benchmarking match B

           Rate ihash    re shash    if
ihash  324969/s    --  -78%  -84%  -84%
re    1473476/s  353%    --  -26%  -28%
shash 2004671/s  517%   36%    --   -2%
if    2053900/s  532%   39%    2%    --

Benchmarking match C

           Rate ihash    re    if shash
ihash  335514/s    --  -76%  -81%  -83%
re    1392243/s  315%    --  -20%  -28%
if    1744756/s  420%   25%    --   -9%
shash 1920959/s  473%   38%   10%    --

[download]

Other possible tests:

Benchmark tests: 

use strict;
use warnings;

use Benchmark    qw( cmpthese );
use Data::Dumper qw( Dumper );
use List::Util   qw( max );

use constant REPS  => $ARGV[0];
use constant COUNT => $ARGV[1];

{
   my $test_if = q{
      my $rv = ($var eq "A" || $var eq 'B' || $var eq 'C');
   };

   my $test_ihash = q{
      my $rv = { A=>1, B=>1, C=>1 }->{$var};
   };

   local our %hash = ( A=>1, B=>1, C=>1 );
   my $test_shash = q{
      our %hash;
      my $rv = $hash{$var};
   };

   my $test_re = q{
      my $rv = $var =~ /^(?:A|B|C)\z/;
   };


   my %tests = (
      if    => $test_if,
      ihash => $test_ihash,
      shash => $test_shash,
      re    => $test_re,
   );


   my $tnl = max map length, keys %tests;


   foreach (values %tests) {
      $_ = q{
         use strict;
         use warnings;
         our $var;
      } . $_;
   }


   {
      print("Compilation tests\n");
      print("\n");

      local our $var = 'moo';

      my $exit;
      foreach my $test (sort keys %tests) {
         printf('%-*s ', $tnl+1, "$test:");
         eval($tests{$test});
         my $e = $@;
         if ($@) {
            chomp($e);
            print("Compile error: $e\n");
            $exit = 1;
         } else {
            print("Compiles ok\n");
         }
      }

      exit(1) if $exit;
   }

   print("\n");
   print("\n");

   {
      print("Benchmarking no matches\n");
      print("\n");

      local our $var = 'D';

      my $exit;
      foreach my $test (sort keys %tests) {
         printf('%-*s ', $tnl+1, "$test:");
         my $rv = eval($tests{$test} . ';$rv');
         if ($rv) {
            local $Data::Dumper::Terse = 1;
            print("Runs error: ", Dumper($test));
            $exit = 1;
         } else {
            print("Runs ok\n");
         }
      }

      last if $exit;

      for (1..REPS) {
         print("\n");
         cmpthese(COUNT, \%tests);
      }
   }

   for (qw( A B C )) {
      print("\n");
      print("\n");

      local our $var = $_;

      print("Benchmarking match $var\n");
      print("\n");

      my $exit;
      foreach my $test (sort keys %tests) {
         printf('%-*s ', $tnl+1, "$test:");
         my $rv = eval($tests{$test} . ';$rv');
         if ($rv) {
            print("Runs ok\n");
         } else {
            local $Data::Dumper::Terse = 1;
            print("Runs error: ", Dumper($test));
            $exit = 1;
         }
      }

      last if $exit;

      for (1..REPS) {
         print("\n");
         cmpthese(COUNT, \%tests);
      }
   }
}

[download]

Complete results: 

>perl -v

This is perl, v5.8.8 built for MSWin32-x86-multi-thread
(with 25 registered patches, see perl -V for more detail)
...
Binary build 817 [257965] provided by ActiveState http://www.ActiveSta
+te.com
Built Mar 20 2006 17:54:25
...

>perl script.pl 3 -3
Compilation tests

shash: Compiles ok
if:    Compiles ok
ihash: Compiles ok
re:    Compiles ok


Benchmarking no matches

shash: Runs ok
if:    Runs ok
ihash: Runs ok
re:    Runs ok

           Rate ihash    re    if shash
ihash  328339/s    --  -79%  -81%  -86%
re    1557274/s  374%    --  -10%  -33%
if    1738308/s  429%   12%    --  -25%
shash 2307394/s  603%   48%   33%    --

           Rate ihash    re    if shash
ihash  341005/s    --  -77%  -81%  -84%
re    1508921/s  342%    --  -16%  -30%
if    1795368/s  426%   19%    --  -16%
shash 2142666/s  528%   42%   19%    --

           Rate ihash    re    if shash
ihash  334628/s    --  -78%  -81%  -86%
re    1508564/s  351%    --  -15%  -37%
if    1778965/s  432%   18%    --  -26%
shash 2405841/s  619%   59%   35%    --


Benchmarking match A

shash: Runs ok
if:    Runs ok
ihash: Runs ok
re:    Runs ok

           Rate ihash    re shash    if
ihash  333900/s    --  -78%  -83%  -88%
re    1532032/s  359%    --  -21%  -43%
shash 1946689/s  483%   27%    --  -28%
if    2707780/s  711%   77%   39%    --

           Rate ihash    re shash    if
ihash  323524/s    --  -80%  -84%  -88%
re    1602110/s  395%    --  -19%  -42%
shash 1990024/s  515%   24%    --  -28%
if    2771856/s  757%   73%   39%    --

           Rate ihash    re shash    if
ihash  337866/s    --  -79%  -83%  -87%
re    1628208/s  382%    --  -17%  -36%
shash 1970859/s  483%   21%    --  -23%
if    2543785/s  653%   56%   29%    --


Benchmarking match B

shash: Runs ok
if:    Runs ok
ihash: Runs ok
re:    Runs ok

           Rate ihash    re shash    if
ihash  324969/s    --  -78%  -84%  -84%
re    1473476/s  353%    --  -26%  -28%
shash 2004671/s  517%   36%    --   -2%
if    2053900/s  532%   39%    2%    --

           Rate ihash    re shash    if
ihash  335927/s    --  -78%  -83%  -84%
re    1520882/s  353%    --  -25%  -28%
shash 2020630/s  502%   33%    --   -4%
if    2100467/s  525%   38%    4%    --

           Rate ihash    re    if shash
ihash  323473/s    --  -78%  -84%  -84%
re    1438394/s  345%    --  -29%  -30%
if    2022373/s  525%   41%    --   -1%
shash 2045609/s  532%   42%    1%    --


Benchmarking match C

shash: Runs ok
if:    Runs ok
ihash: Runs ok
re:    Runs ok

           Rate ihash    re    if shash
ihash  335514/s    --  -76%  -81%  -83%
re    1392243/s  315%    --  -20%  -28%
if    1744756/s  420%   25%    --   -9%
shash 1920959/s  473%   38%   10%    --

           Rate ihash    re    if shash
ihash  329957/s    --  -77%  -81%  -82%
re    1413031/s  328%    --  -17%  -23%
if    1707320/s  417%   21%    --   -7%
shash 1834897/s  456%   30%    7%    --

           Rate ihash    re    if shash
ihash  335803/s    --  -77%  -81%  -83%
re    1452770/s  333%    --  -17%  -26%
if    1747118/s  420%   20%    --  -11%
shash 1967719/s  486%   35%   13%    --

[download]

Replies are listed 'Best First'.
Re^2: Collapsing repetitive equality tests: || vs {} vs // (an observation)
by demerphq (Chancellor) on Feb 25, 2007 at 21:12 UTC

    You missed /^[ABC]\z/ which should be faster than an alternation (but is only viable with one letter options). I also wonder about length($str)==1 && $str=~/[ABC]/

    ---
    $world=~s/war/peace/g

[reply]
[d/l]
[select]

      I took A, B and C to be placeholders for longer strings, so I purposefully didn't include the character class. I even mentioned I should have tested with longer strings as well.

      Feel free to add those tests and publish the results.

[reply]
Re^2: Collapsing repetitive equality tests: || vs {} vs // (an observation)
by blogical (Pilgrim) on Feb 25, 2007 at 11:42 UTC
    Points taken, thank you. As for benchmarking, I did it on the command line, looping over a file of gobbledegook with a `perl -MBenchmark -e`. It was fairly barbaric, compared to what you've posted. I'd still post the exact code if I had it, but cygwin seems to have eaten it.
[reply]

In Section Meditations