leaking into sort when sorting an empty set

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

I have run into an odd sorting issue when sorting an empty set. When you sort an empty list returned from a function, data leaks into a sort call.

use Data::Dumper;
sub foo { return (); }
warn Dumper(sort foo('1000'));
[download]

You would expect that Dumper would print an empty list. However, I get the following:

$VAR1 = '1000';
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This looks like a bug to me but wanted to get more eyes on it first before I added a bug. I've checked both supersearch and perl's bug database without finding a prior report of this issue.

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Re: leaking into sort when sorting an empty set by ikegami (Patriarch) on Mar 21, 2006 at 16:08 UTC
`sort foo('1000');` is the same as `sort foo ('1000');` is the same as `sort foo '1000';` In all of the above, `foo` is used as the compare function to sort the list consisting of `('1000')`. Specifiy a compare function explicitely `sort { $a cmp $b } foo('1000');` or add parenthesises around the arguments to skip the magic `sort(foo('1000'));`	[reply] [d/l] [select]
Re: leaking into sort when sorting an empty set by tilly (Archbishop) on Mar 21, 2006 at 16:10 UTC
Try this: `use Data::Dumper; sub foo { return (); } warn Dumper(sort {$a <=> $b} foo('1000'));` [download] and you get what you expect. Or try: `use Data::Dumper; sub foo { return (); } warn Dumper(sort(foo('1000')));` [download] It looks like Perl thinks that foo is the sort function, and 1000 is what is being passed into the sort. Both those solutions disambiguate the situation.	[reply] [d/l] [select]