I'm looking for an approach that validates floats, or any other complex 'thing' embedded in a string, with a single regex rather than the two-step approach in the example

Generally matching "x but not y" is much harder than matching "x" on its own. The "float but not date" example is a fairly simple case: you can express it as / (?<! [-+.\d]) $re_float (?! [.\d]) /x, but there's quite a bundle of knowledge about the logic of a float getting distilled into that preamble and postamble. Automating that distillation for a generic "this complex thing (but not this other complex thing)" is likely to be somewhere between impossible and unprofitable.

I haven't looked at Friedl since shortly after the first edition was published; I'd certainly recommend having a look through all of perlre and having a play with any construct that is new to you.

More generally: context is everything. What is faster in one context is often slower in a different context. So if you have a problem you're trying to solve for which your existing solution isn't as fast as you want, you should provide it (or something like it) as the benchmark. If you're looking for something that is always better regardless of context, I don't think you'll find it.

For more complex parsing tasks I would also recommend looking at Regexp::Grammars. Making such a grammar fast can take some fiddling, but they make complexity a lot easier to deal with.

In reply to Re^3: Best practice validating numerics with regex? by hv
in thread Best practice validating numerics with regex? by perlboy_emeritus

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • 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:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, 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, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.