perltutorial
tye
<p>
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.
<ol><li>
To use a reference, say $ref, you put <code>{$ref}</code>
in place of a variable <em>name</em> ( not counting the <code>$</code>, <code>%</code>, or <code>@</code> ). That is, replace the variable name with the reference enclosed in braces:
<code>
$scalar ${$sRef}
@array @{$aRef}
$array[0] ${$aRef}[0]
$#array $#{$aRef}
%hash %{$hRef}
$hash{KEY} ${$hRef}{KEY}
@hash{@list} @{$hRef}{@list}
</code>
Note that this works for any expression that returns a reference, not just the simple examples above:
<code>
${$sRefs[0]} ${$sRefs{key}} ${getScalarRef()}
@{$aRefs[0]} @{$aRefs{key}} @{getArrayRef()}
%{$hRefs[0]} %{$hRefs{key}} %{getHashRef()}
@{ $bool ? \%hash1 : \%hash2 }{qw(some keys)}
</code>
</li><li>
If the reference is held in a simple scalar variable, then
the braces, { and }, can be dropped:
<code>
$scalar $$sRef
@array @$aRef
$array[0] $$aRef[0]
$#array $#$aRef
%hash %$hRef
$hash{KEY} $$hRef{KEY}
@hash{@list} @$hRef{@list}
</code></li><li>
If you are getting a <em>scalar</em> from a hash or an array, then you can replace <code>${$ref}</code> with <code>$ref-></code>:
<code>
$array[0] ${$aRef}[0] $aRef->[0]
$hash{KEY} ${$hRef}{KEY} $hRef->{KEY}
</code></li><li>
If the reference is in a hash or an array (and you are getting back a scalar), then you can drop the <code>-></code> between the adjacent <code>[0]</code> and/or <code>{KEY}</code> parts:
<code>
${$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} $hRef->{A}{B}
</code></li></ol><p>
I hope others find this as helpful as I have.
</p><p><small>
Thanks to [arturo] for suggesting that I turn [id://55329] into a tutorial.
</small></p>
-
<a href="/index.pl?node=tye&lastnode_id=1072">tye</a>
(but my friends call me "Tye")
<p>
<small>Thanks to [kutsu] for pointing out that I've had <code>${hRef}{KEY}</code> instead of <code>${$hRef}{KEY}</code> for all these years.</small>
</p>