Earlier use Tk; was already in BEGIN block before the genesis of above test case.

Moving destroy() inside BEGIN does avoid the core dump. Need to have, however, the MainWindow object to live beyond BEGIN block for other things.

#  Remove "BEGIN" and get no core dump.
BEGIN
{
  use Tk;
  our $MW = MainWindow->new();
  # other method calls.
}
our $MW;

# more changes to the window.

#  Being here does not avoid core dump.
$MW->destroy();
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BEGIN
{
  use Tk;
  our $MW = MainWindow->new();
  # other method calls.
}
our $MW;
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Perhaps you mean (not verified):

our $MW;
BEGIN
{
  use Tk;
  $MW = MainWindow->new();
  # other method calls.
}
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Declare the window before the BEGIN block, and assign it within the BEGIN block. Update: I stand corrected.

--MidLifeXis

# cat x.pl ; perl-5.16.2 x.pl

use strict; use warnings FATAL => 'all';
use 5.010;

P::show();
Q::show();
R::show();

{{
  package P;

  my $v = __PACKAGE__;
  BEGIN { $v .= ' ' . __LINE__; }
  sub show { say $v; }
}}

{{
  package Q;

  our $v = __PACKAGE__;
  BEGIN { $v .= ' ' . __LINE__; }
  sub show { say $v; }
}}

{{
  package R;

  BEGIN { our $v = __PACKAGE__ . ' ' . __LINE__; }
  our $v;
  sub show { say $v; }
}}

__END__

 13
 21
R 28
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