Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl-Sensitive Sunglasses

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

I find that the following 4 simple rules cover all of the ways to dereference data structure references. Having the rules spelled out so simply has made using references much less confusing to me.

  1. To use a reference, say $ref, you put {$ref} in place of a variable name ( not counting the $, %, or @ ). That is, replace the variable name with the reference enclosed in braces:
    $scalar ${$sRef} @array @{$aRef} $array[0] ${$aRef}[0] $#array $#{$aRef} %hash %{$hRef} $hash{KEY} ${$hRef}{KEY} @hash{@list} @{$hRef}{@list}
    Note that this works for any expression that returns a reference, not just the simple examples above:
    ${$sRefs[0]} ${$sRefs{key}} ${getScalarRef()} @{$aRefs[0]} @{$aRefs{key}} @{getArrayRef()} %{$hRefs[0]} %{$hRefs{key}} %{getHashRef()} @{ $bool ? \%hash1 : \%hash2 }{qw(some keys)}
  2. If the reference is held in a simple scalar variable, then the braces, { and }, can be dropped:
    $scalar $$sRef @array @$aRef $array[0] $$aRef[0] $#array $#$aRef %hash %$hRef $hash{KEY} $$hRef{KEY} @hash{@list} @$hRef{@list}
  3. If you are getting a scalar from a hash or an array, then you can replace ${$ref} with $ref->:
    $array[0] ${$aRef}[0] $aRef->[0] $hash{KEY} ${$hRef}{KEY} $hRef->{KEY}
  4. If the reference is in a hash or an array (and you are getting back a scalar), then you can drop the -> between the adjacent [0] and/or {KEY} parts:
    ${$aRef->[0]}[1] $aRef->[0]->[1] $aRef->[0][1] ${$aRef->[0]}{KEY} $aRef->[0]->{KEY} $aRef->[0]{KEY} ${$hRef->{KEY}}[1] $hRef->{KEY}->[1] $hRef->{KEY}[1] ${$hRef->{A}}{B} $hRef->{A}->{B} $hRef->{A}{B}

I hope others find this as helpful as I have.

Thanks to arturo for suggesting that I turn references quick reference (Re: push) into a tutorial.

        - tye (but my friends call me "Tye")

Thanks to kutsu for pointing out that I've had ${hRef}{KEY} instead of ${$hRef}{KEY} for all these years.

In reply to References quick reference by tye

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, 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, 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.
  • Log In?

    What's my password?
    Create A New User
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others exploiting the Monastery: (6)
    As of 2020-11-25 14:56 GMT
    Find Nodes?
      Voting Booth?

      No recent polls found