I understand (I think) why this is fast. What I don't understand is how it works. I'll admit that I am not much of regex hacker, but how does the variable length look behind now how far to look, in the case of quantifiers, especially greedy ones? It seems that the goal of the anchor is to prevent backtracking (hence the speed gains) but how does it now when to stop? If the \K anchor tells the regex engine to watch for the oncoming regex and stop matching there, whats the difference between \K and a minimal match, or negated character class? If the engine doesn't stop at the first instance of, say '.' (as in your example) how do you keep it from backtracking (which is where I'm presuming the speed gains come from)? Or is \K an optimization using sexegers?
Now, japhy I have absolute faith in your pattern - foo, so I take it on faith that this works. What I'm curious about is how. Am I missing something in thinking that the performance gains here are related to backtracking?
Light a man a fire, he's warm for a day. Catch a man on fire, and he's warm for the rest of his life. - Terry Pratchet
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:
You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
- a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, 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, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
Link using PerlMonks shortcuts! What shortcuts can I use for linking?
See Writeup Formatting Tips and other pages linked from there for more info.
| & || & |
| < || < |
| > || > |
| [ || [ |
| ] || ] ||