Reference found where even-sized list expected

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

Why does this line:

my %defaults = ref( $_[2+$[] ) ? %{$_[2+$[]} : {};
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get this warning:
Reference found where even-sized list expected at script.pl line 125.
?? The line is the third line of a sub-routine that takes two or three arguments like this:

sub routine 
{
    my %override = %{$_[$[]};  # reference to a hash.
    my $var      = $_[1+$[];   # scalar
    my %defaults = ref( $_[2+$[] ) ? %{$_[2+$[]} : {}; # optional hash
+ ref.
#blah...
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I only get the warning if there is no third argument. ref returns false when given undef, without any warnings as tested via:

prompt> perl -we "print ref( undef() ) ? 'y' : 'n'"
n
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Comment on Reference found where even-sized list expected Select or Download Code

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Re: Reference found where even-sized list expected by btrott (Parson) on Sep 13, 2000 at 23:55 UTC
The ref isn't the problem. The problem is the curly braces, which create an anon hash reference; then you try to assign that to the %defaults hash. So you're assigning a reference, where an even-sized list (a list of key-value pairs) was expected. Hence the error message. Change that line to this: `my %defaults = ref( $_[2+$[] ) ? %{$_[2+$[]} : ();` [download]	[reply] [d/l]
RE: Re: Reference found where even-sized list expected by Adam (Vicar) on Sep 13, 2000 at 23:57 UTC
Oh!!! ++ for btrott and jcwren Once again I fail to understand why someone would down vote a simple node like this one, which was merely posted to say, "Thank you for spotting that which I didn't." After all, isn't that what this site is about? I come here and answer other people's questions, why should I get down voted when I have a question and then take the time to thank the people that spotted the mistake? We all make mistakes. Even the saints and gurus amongst us.	[reply]
(jcwren) Re: Reference found where even-sized list expected by jcwren (Prior) on Sep 13, 2000 at 23:56 UTC
Because the closing brace pair should be parens, since it's an empty hash. Update: Dang! btrott's answer faster AND better... --Chris e-mail jcwren	[reply]