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

Monks, I'm seeing some very odd behavior I think might be a bug (in Moose?) but maybe I'm missing something more basic.

So I've got this line of code:

$event->polished_data->{start} = $event->start_time;

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$event is an object created with Moose, polished_data is an attribute and isa HashRef. $event->start_time is a Time::Piece object. Yes, I am copying the Time::Piece from one part of the object to another.

Here's where the weirdness comes in. After the assignment, when I Dumper the event, sometime the value indexed by the start is the Time::Piece object and and the value of $event->start_time looks like this: $VAR1->{'polished_data'}{'start'}. What's really weird is the rest of the time (about 50% of the time), $event->start_time is the Time::Piece object and the indexed value in the hash is $VAR1->{'polished_data'}{'start'}. Witness:

$VAR1 = bless( {
                 'event_id' => '2927',
                 'post_id' => 0,
                 'polished_data' => {
                                      'start' => bless( [
                                                          0,
                                                          0,
                                                          19,
                                                          28,
                                                          2,
                                                          116,
                                                          1,
                                                          87,
                                                          1,
                                                          1459206000,
                                                          1
                                                        ], 'Time::Piec
+e' ),
                                    },
                 'start_time' => $VAR1->{'polished_data'}{'start'},
               }, 'Event' );

$VAR1 = bless( {
                 'start_time' => bless( [
                                          0,
                                          0,
                                          18,
                                          11,
                                          3,
                                          116,
                                          1,
                                          101,
                                          1,
                                          1460412000,
                                          1
                                        ], 'Time::Piece' ),
                 'polished_data' => {
                                      'start' => $VAR1->{'start_time'}
+,
                                    },
               }, 'Event' );

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If anyone can explain what's going on and help me workaround this issue, I'd greatly appreciate it.

$PM = "Perl Monk's";
$MCF = "Most Clueless Friar Abbot Bishop Pontiff Deacon Curate";
$nysus = $PM . ' ' . $MCF;
Click here if you love Perl Monks

Replies are listed 'Best First'.
Re: Very odd behavior assigning Time::Piece object to hash reference inside of an object
by tangent (Parson) on Mar 24, 2016 at 02:14 UTC
    The behaviour you are seeing is actually a feature of Data::Dumper - the $VAR1->{'polished_data'}{'start'} is simply pointing to the first occurrence of what is exactly the same thing. It does this with all references: 
    use Data::Dumper;
use Time::Piece;

my $tp = gmtime;
my @array = (200,400);

my $data = {
    'one' => {
        'tp' => $tp,
        'array' => \@array,
    },
    'two' => {
        'tp' => $tp,
        'array' => \@array,
    },
};
print Dumper $data;

Output:

$VAR1 = {
  'one' => {
             'array' => [
                          [
                            200,
                            400
                          ]
                        ],
             'tp' => bless( [
                              35,
                              2,
                              2,
                              24,
                              2,
                              '116',
                              4,
                              83,
                              0,
                              1458784955,
                              0
                            ], 'Time::Piece' )
           },
  'two' => {
             'array' => $VAR1->{'one'}{'array'},
             'tp' => $VAR1->{'one'}{'tp'}
           }
};

    [download]
    To prevent it from doing that you can set Deepcopy: 
    use Data::Dumper;
$Data::Dumper::Deepcopy = 1;
...

Output:

$VAR1 = {
  'one' => {
             'array' => [
                          [
                            200,
                            400
                          ]
                        ],
             'tp' => bless( [
                              48,
                              10,
                              2,
                              24,
                              2,
                              '116',
                              4,
                              83,
                              0,
                              1458785448,
                              0
                            ], 'Time::Piece' )
           },
  'two' => {
             'array' => [
                          [
                            200,
                            400
                          ]
                        ],
             'tp' => bless( [
                              48,
                              10,
                              2,
                              24,
                              2,
                              '116',
                              4,
                              83,
                              0,
                              1458785448,
                              0
                            ], 'Time::Piece' )
           }
};

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      Thank you for clearing this up.

      $PM = "Perl Monk's";
      $MCF = "Most Clueless Friar Abbot Bishop Pontiff Deacon Curate";
      $nysus = $PM . ' ' . $MCF;
      Click here if you love Perl Monks

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