package Application::Option;

use strict;
use warnings;

use Tk;

use version;

...

# firstly, create subroutines that do the right thing for various Tk versions

# poulate Listboxes with modern Tk's
sub renderListAutoPopulate {
  my (undef, $parentWidget, $listVariable) = @_;

  return $parentWidget->Listbox(
                                -listvariable => $listVariable, # autopopulate from this list
		                # other options as required
		               )->pack(
			               # pack options
			              );
}

# populate old Tk Listboxes
sub renderListManualPopulate {
  my (undef, $parentWidget, $listVariable) = @_;

  my $thisListbox = $parentWidget->Listbox(
				           # options as required
				    )->pack(
					    # pack options
					   );

  $thisListbox->insert('end', @$listVariable);


  return $thisListbox;
}

# present numeric options with modern Tk Spinbox

sub renderNumericOptionAsSpinbox {
  my (undef, $parent, $value) = @_;

  $parent->Spinbox(
                   # spinbox options as required
		  )->pack(
			  # pack options
			 );
}

# present numeric option as a Tk::Entry widget, for older Tk's
sub renderNumericOptionAsEntry {
  my (undef, $parent, $value) = @_;

  $parent->Entry(
                 # Entry options as required
                )->pack(
			# pack options
		       );
}

# secondly, populate typeglobs with the required function references
# version.pm overloads relational and stringification operators conveniently
INIT {
 if (qv(Tk->VERSION()) >= "804.027") { # modern Tk
   *numericWidget = \&renderNumericOptionAsSpinbox;
   *listboxWidget = \&renderListAutoPopulate;
 } else { # older-style Tk
   *numericWidget = \&renderNumericOptionAsEntry;
   *listboxWidget = \&renderListManualList;
 }
}

# thirdly, call the code slot in the typeglob as required in the application

...

} elsif (numericOption($option)) {
 $self->numericWidget($parent, $option);
} elsif (listboxOption($option)) {
 $self->listboxWidget($parent, $option);
} elsif (# other  option types

...