This intigued me and I thought maybe the 7.5% difference was in the time it took to parse and/or compile the differences in the regexes. So I thought I'd benchmark the test with them pre-compiled. The results are very intriguing. Not only does the difference between the two compiled versions remain pretty much the same, if anything getting slightly bigger. The pre-compiled versions actually run substantially more slowly than their none pre-compiled counterparts? This is most extreme in the case of the (foob|) version running close to 40% faster than its precompiled counterpart.

I'd like to see the explanation behind them onions? Probably my test methodology at fault, but I can't see it.

It took that a stage further and applied study to the searched string. This resulted in a speed-up of the slowest (precompiled (foob)?) and the fastest (the non-precompiled (foob|)), but consistantly slowed the other two varients down.

Intriguing indeed. The test code and results are below 

#!/usr/bin/perl
no warnings;
use strict;
use Benchmark qw(cmpthese);

$::string = "foofoo catbar";
$::re_foobOrNowt     = qr/(foob|)foofoo/o;
$::re_foob0or1        = qr/(foob)?foofoo/o;

#study $::string; print 'After studying the searched string'.$/;
cmpthese( 1000000, {
    foobOrNowt    => 'if ($string =~ m/(foob|)foofoo/) { };',
    foob0or1    => 'if ($string =~ m/(foob)?foofoo/) { };',
    c_foobOrNowt=> 'if ($string =~ $::re_foobOrNowt) { };',
    c_foob0or1    => 'if ($string =~ $::re_foob0or1  ) { };',
});

__DATA__

C:\test>201403
Benchmark: timing 1000000 iterations of c_foob0or1, c_foobOrNowt, foob
+0or1, foobOrNowt...
c_foob0or1: 13 wallclock secs (13.38 usr +  0.00 sys = 13.38 CPU) @ 74
+744.00/s (n=1000000)
c_foobOrNowt: 12 wallclock secs (11.85 usr +  0.00 sys = 11.85 CPU) @ 
+84409.56/s (n=1000000)
  foob0or1: 10 wallclock secs (10.63 usr +  0.00 sys = 10.63 CPU) @ 94
+117.65/s (n=1000000)
foobOrNowt:  8 wallclock secs ( 8.60 usr +  0.00 sys =  8.60 CPU) @ 11
+6238.52/s (n=1000000)
                 Rate   c_foob0or1 c_foobOrNowt     foob0or1   foobOrN
+owt
c_foob0or1    74744/s           --         -11%         -21%         -
+36%
c_foobOrNowt  84410/s          13%           --         -10%         -
+27%
foob0or1      94118/s          26%          12%           --         -
+19%
foobOrNowt   116239/s          56%          38%          24%          
+ --

C:\test>201403
After studying the searched string
Benchmark: timing 1000000 iterations of c_foob0or1, c_foobOrNowt, foob
+0or1, foobOrNowt...
c_foob0or1: 12 wallclock secs (12.57 usr +  0.00 sys = 12.57 CPU) @ 79
+567.15/s (n=1000000)
c_foobOrNowt: 12 wallclock secs (11.67 usr +  0.00 sys = 11.67 CPU) @ 
+85711.84/s (n=1000000)
  foob0or1: 11 wallclock secs (10.65 usr +  0.00 sys = 10.65 CPU) @ 93
+940.82/s (n=1000000)
foobOrNowt: 10 wallclock secs ( 8.42 usr +  0.00 sys =  8.42 CPU) @ 11
+8736.64/s (n=1000000)
                 Rate   c_foob0or1 c_foobOrNowt     foob0or1   foobOrN
+owt
c_foob0or1    79567/s           --          -7%         -15%         -
+33%
c_foobOrNowt  85712/s           8%           --          -9%         -
+28%
foob0or1      93941/s          18%          10%           --         -
+21%
foobOrNowt   118737/s          49%          39%          26%          
+ --

C:\test>

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In reply to Re: Difference between (foo|) and (foo)? by BrowserUk
in thread Difference between (foo|) and (foo)? by Derek2

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