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Perl references - $$var and \$var notations

Perl references - $$ and $In Perl, if I write:
$stuff = "Porridge";
then I'm setting up a variable to contain the value "Porridge".

If I write:
$stuffat = \$stuff;
then I'm setting up a variable to contain the ADDRESS OF the variable $stuff.

So if $stuff was in memory at (hex)fe80 ... then $stuffat will be assigned that value 0xfe80. And we can look use it by using an extra $ character :
print $$stuffat;
which literally means "the contents of the contents of stuffat".


What use is this?

Lots ... not only for scalars, but for the addresses of lists too. If I write
$holder = \@biglist;
I have assigned a single scalar variable to point to what is potentially a huge dataset and (for starters) I can easily pass it around to various subs without the need to replicate the data.

Other languages have this concept - "pointer" - too. See & and * in C, and the use of & in PHP.
(written 2009-06-15 14:00:42)

 
Associated topics are indexed under
P217 - Perl - More than Simple Lists and Hashes!
  [1514] Autovivification - the magic appearance of variables in Perl - (2008-01-21)
  [293] Course follow-ups - (2005-04-27)
  [43] Hash of lists in Perl - (2004-09-09)

P301 - Variables in Perl
  [2374] Lead characters on Perl variable names - (2009-08-24)
  [1946] Variable Types in Perl - (2008-12-15)
  [1581] What is an lvalue? (Perl, C) - (2008-03-18)
  [975] Answering ALL the delegate's Perl questions - (2006-12-09)


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