From the I learn new things about Perl every day department.

On the Paris.pm list today, someone wrote (translated):

> my %opts;
> getopts('hf:d:', \%opts);

my() is an operator like any other, syntactically speaking:

    getopts('hf:d:', \my %opts);

Since a function call doesn't define a new scope (until one enters the function), the above works just fine and the code snippets appear to be functionally equivalent, though they deparse slightly differently:

$ perl -MO=Deparse -e 'foo(\my $bar)'
foo \my($bar);
-e syntax OK

$ perl -MO=Deparse -e 'my $bar; foo(\$bar)'
my $bar;
foo \$bar;
-e syntax OK

[download]

I was pleasantly surprised by this and sort of like the idea of defining an variable like this, but I suspect that this might be obfuscated and potentially bug prone. For example, the following code might look like both hashes should have the value of 2 for the key 'foo'. They don't.

#!/usr/bin/perl
use strict;
use Data::Dumper;

my %hash1 = ( foo => my ($bar) );
$bar = 2;

my %hash2 = ( foo => \my $bar2 );
$bar2 = 2;

print Data::Dumper->Dump([\%hash1,\%hash2], [qw(*hash1 *hash2)]);

[download]

The first hash has undef for the value of 'foo' because my appears to return what it's declaring. The second hash has a reference to the value of $bar and by dereferencing it, you can get to the value. Thus, if you take a reference to my, you get a reference to the declared variable and if you're declaring a list, you get a reference to each item of the list.

my $ref = \my $foo;
printf  $ref eq \$foo ? "Same address\n" : "Not same address\n";

my @array = \my ($this, $that);
$this = "Ovid";
print Data::Dumper->Dump([\@array,$this,$that], [qw(*array *this *that
+)]);

[download]

Is there a particular use for this other than obfuscation and are there any 'gotchas' that one should be aware of?

Cheers,
Ovid

New address of my CGI Course.
Silence is Evil (feel free to copy and distribute widely - note copyright text)

In reply to Referencing built-ins by Ovid

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