Dear Perl Monks

I'm getting the message

Operation "<=>": no method found,
  left argument in overloaded package Class::Measure::Length,
  right argument in overloaded package Class::Measure::Length

[download]

from what I thought was just a simple sort

$hash{$b}<=>$hash{$a}

I found a work-around, by sprintf-ing the values in the hash - see code below - but I would like to (try to) understand what is going on.

I'm on Ubuntu 12.04

perl -v says

This is perl 5, version 14, subversion 2 (v5.14.2)
built for i686-linux-gnu-thread-multi-64int

[download]
The following script gives the no method found message the second time round 
use strict;
use Carp;
use GIS::Distance;

my $from_lat  = 50.815717;
my $from_long = 4.436326;

my $to = {
    Montana => [ 46.536026, -111.935062 ],
    Correze => [ 45.341874, 1.79531 ],
    ParisFR => [ 48.850407, 2.347304 ],
};

my %distance;
foreach my $demo ( 'solution', 'problem' ) {
    print STDOUT "\n", "-" x 60, "\n\n";
    print STDOUT "This is to demonstrate the $demo ...\n";
    print STDOUT "  Here comes the contents of the hash \%distance\n";
    print STDOUT "  (distances as calculated by GIS::Distance\n";
    if ( $demo eq 'problem' ) {
        print STDOUT "  and stored as that value)\n";
    }
    elsif ( $demo eq 'solution' ) {
        print STDOUT "  and stored as sprintf \"%25.15f\", value )\n";
    }
    foreach my $place ( keys(%$to) ) {
        my $gis     = GIS::Distance->new();
        my $to_lat  = $to->{$place}->[0];
        my $to_long = $to->{$place}->[1];
        my $km = $gis->distance( 
            $from_lat, $from_long => $to_lat, $to_long, );
        if ( $demo eq 'problem' ) {
            $distance{$place} = $km;
        }
        elsif ( $demo eq 'solution' ) {
            $distance{$place} = sprintf "%25.15f", $km;
        }
        print STDOUT "  \$distance{$place} = $distance{$place}\n";
    }
    print STDOUT "\n";
    print STDOUT
      "And here comes the result of sorting the keys of that hash\n";
    foreach
      my $place(sort
       {$distance{$b} <=> $distance{$a}}( 
        keys(%distance)))
    {
        printf STDOUT "%10s is %25.15f km from here\n",
        $place, $distance{$place};
    }
}

[download]

In reply to Why am I getting message «Operation "<=>": no method found,» ? by RCH

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