NAME
    Devel::SawAmpersand - Perl extension querying sawampersand variable

SYNOPSIS
      use Devel::SawAmpersand qw(sawampersand);

      sawampersand();

DESCRIPTION
    There's a global variable in the perl source, called sawampersand. It
    gets set to true in that moment in which the parser sees one of $`, $',
    and $&. It never can be set to false again. Trying to set it to false
    breaks the handling of the $`, $&, and $' completely.

    If the global variable "sawampersand" is set to true, all subsequent RE
    operations will be accompanied by massive in-memory copying, because
    there is nobody in the perl source who could predict, when the
    (necessary) copy for the ampersand family will be needed. So all
    subsequent REs are considerable slower than necessary.

    There are at least three impacts for developers:

    *   never use $& and friends in a library.

    *   Don't "use English" in a library, because it contains the three bad
        fellows. Corollary: if you really want to use English, do it like
        so:

            use English qw( -no_match_vars ) ;

    *   before you release a module or program, check if sawampersand is set
        by any of the modules you use or require.

  Workaround
    Fortunately perl offers easy to use alternatives, that is

           instead of this              you can use this

         $`   of   /pattern/          $1   of  /(.*?)pattern/s
         $&   of   /pattern/          $1   of  /(pattern)/
         $'   of   /pattern/          $+   of  /pattern(.*)/s

    In general, apply "/^(.*)(pattern)(.*)$/s" and use $1 for $`, $2 for $&
    and $+ for $' ($+ is not dependent on the number of parens in the
    original pattern). Note that the "/s" switch can alter the meaning of
    "." in your pattern.

  Future Directions
      From: jmm@elegant.com (John Macdonald)
      Date: Wed, 24 Dec 1997 10:49:56 -0500

    How about adding an option to matches/substitutes that explicitly sets
    $`, $&, and $'? When this new option is seen, sawampersand will be set
    for the duration of the match and then turned off. That causes the
    expense for unflagged matches to go back to normal and only flagged
    matches incur the extra expense and they would be the ones that actually
    need it. (Or does sawampersand need to affect the compilation of the
    RE's too?)

AUTHOR
    Andreas Koenig, special thanks to Johan Vromans and John Macdonald for
    parts of the manpage and to Doug MacEachern for the FindAmpersand.

SEE ALSO
    Devel::FindAmpersand, B::FindAmpersand