I just picked up the new second edition of Mastering Regular Expressions and was marveling at how much regex support exists in other languages, features I didn't know existed, and - boggle of boggles - something java did better(?) than perl.

Particularly, I looked at what he dubbed 'atomic grouping' with great interest. Perl appears to support it as the (?>) operator. Java supports it in a shorter manner by just adding a + onto another quantifier (++ *+ ?+ {m,n}+) and calls it the 'possessive quantifier'. For those of you who, like me, had never run into this critter before, the simple explanation is this:

Possessive quantifiers take the greedy quantifiers and tell them to never let go of anything they've grabbed. Potentially, they can make matches faster by eliminating unnecessary backtracking.

I lit on atomic grouping as a useful feature, found it documented logically yet rather quietly as 'match nonbacktracking subpattern' in the Camel 3. The possessive extra '+' seemed like a convenient shortening for many purposes. Many questions have sprouted in my mind:

  1. Are Those Who Make The Changes plan on adding the possessive quantifiers (++ *+ ?+ {m,n}+) to the regex engine in 5.10?
  2. To give this node an additional purpose, does anyone have some particularly good examples of when they have used possessive quantifiers or (?>) in Real Life (tm)?
  3. Lastly, does anyone know how to cure the desire to treat the above "(tm)?" as zero-or-one occurences of the string 'tm', captured? I think I've got REs on the brain. :-)

Edit: Fixed broken link. larsen

In reply to Possessive Quantifiers by Ferret

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