http://www.perlmonks.org?node_id=1038684

zork42 has asked for the wisdom of the Perl Monks concerning the following question:

I accidentally typed "my ($x) = @);" instead of "my ($x) = @_;"
Shouldn't the former have generated a syntax error?
use strict;
use warnings;

foo(1);

sub foo
{
    my ($x) = @);   # why doesn't this generate a syntax error?
    print $x;
}

# Program Output: "Use of uninitialized value $x in print at test.pl l
+ine 9."

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perlvar.html says there is a "$)" variable, but "@)" is not mentioned.
I suspect I've missed something obvious, but I can't see what!

Replies are listed 'Best First'.
Re: Why doesn't "my ($x) = @);" generate a syntax error?
by tobyink (Canon) on Jun 13, 2013 at 06:50 UTC

    For any punctuation character x, if there is a magic variable called $x, then there must also be magic variables called @x and %x. That's an artefact of how current versions of the Perl parser work. So because the $) exists and does something useful, the @) variable must also exist (even if it does nothing useful!)

    package Cow { use Moo; has name => (is => 'lazy', default => sub { 'Mooington' }) } say Cow->new->name
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      Correction: for any punctuation character x except '[' and '{', there exist global variables $x, @x and %x. Those variables are not necessarily magic, and their existence doesn't depend on the fact that $x does something useful. For example, none of $}, @} and %} are magic, yet they are all global variables.
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        $[, @[ and %[ work (or at least they do in 5.18.0). If ${, @{ and %{ were to work, that would break dereferencing.

        package Cow { use Moo; has name => (is => 'lazy', default => sub { 'Mooington' }) } say Cow->new->name
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      I'd have never realised that.
      Thanks!
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