I can't reproduce this, the output includes the "Can't vivify reference" error under both versions of Perl. Perhaps you're using different versions of the autovivification module?

And what would be the proper way to check existence of value in last line in ver 5.28?

The proper core-only way to check in any version of Perl is exists $$h{a} && exists $$h{a}{x} && exists $$h{a}{x}{z}. Using exists allows you to differentiate between a key not existing, a key existing and its value not being defined, and a key existing and having a false value. With no autovivification and if you know your values are always true, I guess you could say $$h{a} && $$h{a}{x} && $$h{a}{x}{z}, but I don't have much experience with that module.

Note that there are other modules you can use to look at data structures without autovivifying them, without changing the behavior of core Perl, such as Data::Diver.

In reply to Re: 5.24 -> 5.28 -- what has changed in autovivification? by haukex
in thread 5.24 -> 5.28 -- what has changed in autovivification? by leszekdubiel

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.