/o can still be useful from time to time. Firstly, you occasionally expect that the interpolated variable may change but still want to use the original value (but this is rare). Secondly, the "recompile only if changed" logic requires checking whether the pattern has changed, which takes time: 

  perl -MBenchmark -w
    ($s, $t) = qw/ foo xfoox /;
    timethese(-1, {
      oful => q{ $t =~ /$s/o },
      oless => q{ $t =~ /$s/ },
    })
  __END__
  Benchmark: running oful, oless for at least 1 CPU seconds...
        oful:  2 wallclock secs ( 1.08 usr +  0.00 sys =  1.08 CPU) @ 
+2427258.33/s (n=2621439)
       oless:  2 wallclock secs ( 1.15 usr +  0.00 sys =  1.15 CPU) @ 
+1841144.35/s (n=2117316)

[download]

Hugo

In reply to Re^3: Compiling Regular Expressions by hv
in thread Compiling Regular Expressions by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.