Special literals taken literally

Sometimes, mistakes stare you in the face and you still miss them. This brief meditation is on the topic of special literals, one of which recently caused a frustrating bug for me. Realizing what had happened was a bracing reminder about when to use the cruciform operator.

For beginning to intermediate monks, ponder the following code snippet:

# In the file 'literal.pl'
package Illumination;
use strict;
use warnings;
use Data::Dumper;

my %hash;
$hash{__PACKAGE__}{__FILE__}{__LINE__} = "Mu Mu";

print Dumper \%hash;
[download]

What will it produce? Check your answer.

-xdg

Code written by xdg and posted on PerlMonks is public domain. It is provided as is with no warranties, express or implied, of any kind. Posted code may not have been tested. Use of posted code is at your own risk.

Comment on Special literals taken literally Download Code
Re: Special literals taken literally by bobf (Monsignor) on Apr 14, 2006 at 03:58 UTC
Interesting. Apparently, I would have made the same mistake you did. :-) <Reveal this spoiler or all in this thread> Double-cruciform (++) for the reminder.	[reply] [d/l] [select]
Re: Special literals taken literally by diotalevi (Canon) on Apr 14, 2006 at 05:38 UTC
Well, err, yeah. Shouldn't this have been obvious to you? Fat comma has the same effect. That hash subscripts are treated as strings is nothing new. You've known you can type `$foo{BAR}` without having to quote "BAR". This is just the same rule. No special magic at all. In fact, that's thing. There's less magic here. ⠤⠤ ⠙⠊⠕⠞⠁⠇⠑⠧⠊	[reply] [d/l]
Re^2: Special literals taken literally by xdg (Monsignor) on Apr 14, 2006 at 12:56 UTC
Well, err, yeah. Shouldn't this have been obvious to you? Yes, it should have. I kicked myself when I realized what I did. This meditation is a reminder, not a discovery. -xdg Code written by xdg and posted on PerlMonks is public domain. It is provided as is with no warranties, express or implied, of any kind. Posted code may not have been tested. Use of posted code is at your own risk.	[reply]
Re: Special literals taken literally by larryl (Scribe) on Apr 14, 2006 at 16:42 UTC
Good point - I was recently similarly burned by something like this: `use constant FOO => 'my hash key'; my %hash = ('my hash key' => 42); print "Wahoo!\n" if exists $hash{FOO};` [download] This will work as expected: `print "Wahoo!\n" if exists $hash{+FOO};` [download] Larry	[reply] [d/l] [select]
Re: Special literals taken literally by TimToady (Parson) on Apr 14, 2006 at 22:51 UTC
Interestingly, this is fixed two different ways in Perl 6. Instead of special tokens, we have compiler variables like `$?PACKAGE` and `$?FILE`. And even if they were still bare identifiers, it would still work, because curlies no longer autoquote. We now use a different notation (angle brackets) for constant string subscripts. Sorry, I usually try to resist saying "fixed in six", because you'd get tired of it if we said it as often as it's true...	[reply]


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Special literals taken literally

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