package personel;

use warnings;
use strict;


sub sortAge { $b->[1] <=> $a->[1]; }

sub cmpAge1 { $main::b->[1] <=> $main::a->[1]; }
sub cmpAge2 { $::b    ->[1] <=> $::a    ->[1]; }

sub cmpAge3 {  # slower
    my $callingPkg = caller;
    no strict 'refs';
    ${"$callingPkg\::b"}->[1] <=> ${"$callingPkg\::a"}->[1];
  # ${"${callingPkg}::b"}->[1] <=> ${"${callingPkg}::a"}->[1];  # also works
    }


return 1;

##</code><code>##

use warnings;
use strict;


use personel;
use Data::Dump;


my @personnel = (
    [ 'amy', 35 ], [ 'bill', 55 ], [ 'george', 28 ], [ 'jason', 71 ],
    );

print "doesn't work: \n";
my @not_sorted_by_age = sort personel::sortAge @personnel;
dd \@not_sorted_by_age;
print "\n";

print "does work: \n";
my @sorted_by_age_descending1 = sort personel::cmpAge1 @personnel;
dd \@sorted_by_age_descending1;
print "\n";

print "also works: \n";
my @sorted_by_age_descending2 = sort personel::cmpAge2 @personnel;
dd \@sorted_by_age_descending2;
print "\n";

print "also works (somewhat slower): \n";
my @sorted_by_age_descending3 = sort personel::cmpAge3 @personnel;
dd \@sorted_by_age_descending3;
print "\n";

print "original array (should be unchanged): \n";
dd \@personnel;
print "\n";

##</code><code>##

c:\@Work\Perl\monks\polmed>perl test.pl
doesn't work:
Use of uninitialized value in numeric comparison (<=>) at personel.pm line 7.
Use of uninitialized value in numeric comparison (<=>) at personel.pm line 7.
Use of uninitialized value in numeric comparison (<=>) at personel.pm line 7.
Use of uninitialized value in numeric comparison (<=>) at personel.pm line 7.
Use of uninitialized value in numeric comparison (<=>) at personel.pm line 7.
Use of uninitialized value in numeric comparison (<=>) at personel.pm line 7.
Use of uninitialized value in numeric comparison (<=>) at personel.pm line 7.
Use of uninitialized value in numeric comparison (<=>) at personel.pm line 7.
[["amy", 35], ["bill", 55], ["george", 28], ["jason", 71]]

does work:
[["jason", 71], ["bill", 55], ["amy", 35], ["george", 28]]

also works:
[["jason", 71], ["bill", 55], ["amy", 35], ["george", 28]]

also works (somewhat slower):
[["jason", 71], ["bill", 55], ["amy", 35], ["george", 28]]

original array (should be unchanged):
[["amy", 35], ["bill", 55], ["george", 28], ["jason", 71]]