I agree that the explanatory text is a bit nutty, but there is a reason. It's not so that the code will work correctly, or better, or whatnot. It's so that you won't cause a memory leak if you reference the code again and again.

As a demonstration, put the above code inside a sub, and then have something that calls that subroutine, say, 16_000_000 times. (Call it on the same very, very small tree - I recommend a tree that's no more than one element in size)

Now try the same thing without the undef.

The difference between the two sets of examples he gives is that the bad examples create a reference from $give_id to itself - that is, they create a recursive data structure. Perl's garbage collector doesn't handle recursive structures, so you shouldn't leave them around after a variable goes out of scope.

In reply to Re: Q on HTML::Element recursive lambda comment by fizbin
in thread Q on HTML::Element recursive lambda comment by lucylane

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.