SPUG: SQL syntax Regular Expression

Colin Meyer cmeyer at helvella.org
Sat Jun 22 11:34:39 CDT 2002


Hi Tim,

On Thu, Jun 20, 2002 at 09:15:05AM -0700, SPUG-list-owner wrote:
> On Thu, Jun 20, 2002 at 12:21:17AM +0000, Dan Sanderson wrote:
> > 
> > This may or may not be worth mentioning in this particular case, but since
> > I learned this lesson the hard way, I feel like mentioning it every time I
> > see $` and $' (and $&) mentioned.  From camel, 24.2.1:
> > 
> >  Avoid $& and its two buddies, $` and $'. Any occurrence in your program
> >  causes all matches to save the searched string for possible future
> >  reference. (However, once you've blown it, it doesn't hurt to have more
> >  of them.)
> 
> It's page 146 in the 3rd edition, which makes it clear that capturing
> parens have the same performance hit too, and you hardly see people
> becoming zealots in their avoidance!

The difference is that using $` or $' make *every* regex take the
performance hit. Using capturing parens only effect the regex[s] that
they appear in.

  "... if you never use $`, $&, or $', then patterns without capturing
  parentheses will not be penalized."

Have fun,
-C.

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