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

use Data::Dumper;

{   package MyClass;
    use DateTime;

    sub foo {
        my ($self,$input) = @_;
        my @ymd = split("-",$input);

        my $date = {
                    day => $ymd[2],
                    month => $ymd[1],
                    year => $ymd[0],
                   };

        my $dt = eval{DateTime->new($date)};
        return unless $dt;

        $date->{dt} = $dt;
        return $date
    }

    sub new { bless {}, shift }

}

my $dt = 'MyClass'->new;
my $result = $dt->foo('2001-01-01');
print Dumper $result;
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Output:

$VAR1 = {
          'dt' => bless( {
                           'utc_rd_days' => 730486,
                           'rd_nanosecs' => 0,
                           'local_rd_days' => 730486,
                           'utc_rd_secs' => 0,
                           'locale' => bless( {
                                                'native_complete_name'
+ => 'English United States',
                                                'en_territory' => 'Uni
+ted States',
                                                'en_language' => 'Engl
+ish',
                                                'en_complete_name' => 
+'English United States',
                                                'native_territory' => 
+'United States',
                                                'default_time_format_l
+ength' => 'medium',
                                                'default_date_format_l
+ength' => 'medium',
                                                'id' => 'en_US',
                                                'native_language' => '
+English'
                                              }, 'DateTime::Locale::en
+_US' ),
                           'utc_year' => 2002,
                           'formatter' => undef,
                           'offset_modifier' => 0,
                           'local_c' => {
                                          'day_of_quarter' => 1,
                                          'day' => 1,
                                          'day_of_year' => 1,
                                          'hour' => 0,
                                          'second' => 0,
                                          'quarter' => 1,
                                          'minute' => 0,
                                          'year' => 2001,
                                          'month' => 1,
                                          'day_of_week' => 1
                                        },
                           'local_rd_secs' => 0,
                           'tz' => bless( {
                                            'offset' => 0,
                                            'name' => 'floating'
                                          }, 'DateTime::TimeZone::Floa
+ting' )
                         }, 'DateTime' ),
          'month' => '01',
          'day' => '01',
          'year' => '2001'
        };
[download]

Given only your code and your description that the print statement works, that does seem quite strange. Have you stepped through the code in the debugger? Can you reduce your code down to an example that reproduces the problem that you can post here for others to run?

(By the way, DateTime::Format::Strptime can handle what your sub foo is doing.)

return unless $dt;

Exactly what are you returning here unless $dt is true?

-- FloydATC

Time flies when you don't know what you're doing

But look at where the print statement is which the OP claims works...

What is the class of $date_thingy and in which class is sub foo defined? Does the class in which sub foo is defined have a subclass that overrides sub foo? Are there any other things in your code that share the name foo?