What matters is the value of $word, because we're using the value of $word to compile the regexp. While the value of the variable to which $word is/was aliased doesn't change, the value of $word itself does change.

In the first pass, $word is "foo". The regexp was thus compiled with to /foo/. In the second pass, $word is "bar". We obviously need to recompile the regexp because we want /bar/ and it's currently /foo/. Whether $words[0] and $words[1] changed or not is completely irrelevant.

You might be thinking that the compiled regexp is stored with the variable used in the regexp. It's not. That wouldn't work when no variables or multiple variables are used to create the regexps. Instead, the uncompiled regexp or the values of the variables used to compile the regexp -- I don't know which -- is stored along with the compiled regexp in the code.

In reply to Re^5: speeding up a regex by ikegami
in thread speeding up a regex by Anonymous Monk

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.