Beefy Boxes and Bandwidth Generously Provided by pair Networks
No such thing as a small change

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":

  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or How to display code and escape characters are good places to start.
Log In?

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

How do I use this?Last hourOther CB clients
Other Users?
Others chanting in the Monastery: (1)
As of 2023-11-29 02:51 GMT
Find Nodes?
    Voting Booth?

    No recent polls found