use 5.010;
 ...

my %params;
my @parts = split '.', $mystring;
$params{cheese} = $parts[0];
$params{country} = $parts[1];
$params{state} = $parts[2];
$params{town} = $parts[3];

doSumpton(%params);

 ...

sub doSumpton {
    my %params = @_;

    $params{cheese} //= '-- bad cheese --'; # Provide cheesy default
    print "Cheese: $params{cheese}\n";
}