#!/usr/bin/perl --
use strict; use warnings; use Data::Dump qw/ dd /;
{ package Foo; sub Foo::comp { $b <=> $a } }
{ package Oof; sub Oof::comp { $::b <=> $::a } }
sub pomc { $b <=> $a }
dd( [ sort { pomc() } 1..10 ] );
dd( [ sort { Foo::comp() } 1..10 ] );
{
  my @f  = 1..10;
  my $cb = \&Foo::comp;
  dd( [ sort $cb @f ] );
  $cb = \&pomc;
  dd( [ sort $cb @f ] );
  $cb = \&Oof::comp;
  dd( [ sort $cb @f ] );
}
__END__