$ret{$j}[$i]

[download]
is short for 
$ret{$j}->[$i]

[download]

In lvalue context (e.g. on the left of a "="), -> and other dereference operators will autovivify the reference. That means dereference operators will automatically create a variable of the required variable type (e.g. ->[...] will create a hash) and place a reference to it in the variable being dereferenced. This only happens if the variable being dereferenced is undef. In other words, 

$ret{$j}[$i]

[download]
is short for 
( $ret{$j} //= [] )->[$i]

[download]

when used as an lvalue.

In reply to Re: which line(s) establishes a 2d arrray by ikegami
in thread which line(s) establishes a 2d arrray by DanielM0412

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.