comment on

Anyone who does anything significant with regular expressions learns that the variables $&, $' and $` imposes significant performance penalty on all regular expression matches. I have personally witnessed just how significant the use of these variables can be on performance (KinoSearch & Large Documents).

perlvar says under @- the following:

$`  is the same as substr($var, 0, $-[0])
$& is the same as substr($var, $-[0], $+[0] - $-[0])
$' is the same as substr($var, $+[0])
[download]

So my question is why can't these variables be implemented this way behind the scenes. If I could get access to the last variable successfully matched against, for instance, I could write a Tie interface for these variables very easy.

I am guessing it has to do with keeping track of the last variable matched and handling cases where that variable is changed before reading $& (such as assignment or a s///).

This question is really out of curiosity about the internals of the perl regexp engine.

Thanks,

Ted Young

($$<<$$=>$$<=>$$<=$$>>$$) always returns 1. :-)

In reply to Can we make $& better? by TedYoung

Are you posting in the right place? Check out Where do I post X? to know for sure.
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
Want more info? How to link or How to display code and escape characters are good places to start.


more useful options
	PerlMonks