I've found an odd bit of behavior when I assign a list to a hash within a subroutine. When the following conditions are met, the resulting hash will not contain all of the keys that were assigned to it.

1) The hash is defined within a subroutine

2) The list assigned to the hash contains a duplicate key

3) The hash is returned out of the subroutine without 'return'.

The following code demonstrates this. The first hash contains all ten keys (one is duplicated) while the second contains only eight keys. 

#!/usr/bin/perl
use strict;
use warnings;

my %hash = (
        "A" => 1,
        "B" => 1,
        "C" => 1,
        "D" => 1,
        "E" => 1,
        "B" => 1,
        "F" => 1,
        "G" => 1,
        "H" => 1,
        "I" => 1,
        "J" => 1,
);

for my $key (sort(keys(%hash))) {
        print "$key\n";
}

my %hash2 = makesubhash();

print "_"x10,"\n";

for my $key (sort(keys(%hash2))) {
        print "$key\n";
}


sub makesubhash {
        my %subhash = (
                "A" => 1,
                "B" => 1,
                "C" => 1,
                "D" => 1,
                "E" => 1,
                "B" => 1,
                "F" => 1,
                "G" => 1,
                "H" => 1,
                "I" => 1,
                "J" => 1,
        );
}

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If you remove the duplicate key (B), or explicitly 'return %subhash' the problem will not occur. Normally I use explicit returns all the time, but I stumbled across this and thought it was odd.

Is there a good reason for this behavior? Have I stumbled across a bug in perl?

EDIT: I'm using perl version 5.8.5. I've removed the DateTime module from the code; didn't mean to include it. The output looks like this: 

A
B
C
D
E
F
G
H
I
J
__________
B
C
D
E
F
G
H
I

[download]

In reply to Missing Hash Keys When Hash Created in Sub by Stringer

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