hey all--

I'm working on a method in my first OO project which seems like it should be simple but ended up pretty complex (and still doesn't DWIW). The idea is that I only want to allow certain values to be passed as parameters, and I want to assign a default if the value passed is not one of the legal ones. Here my attempted WTDI:

#! perl -w
use strict;

package Test;

sub new {
    my $class = $_[0];
    my $self = {'associations' => undef,
            'balance_by' => undef,
        'comment' => undef};
    
    bless $self, $class;
    return $self;
}

sub balance_by {
    my $self = shift;
    my $entry = shift;
    my %valid_params = map {$_ => 1} ('foo',
                      'bar');

    unless (defined $self->{'balance_by'}) {
    $self->{'balance_by'} = 
        (defined $entry && $valid_params{$entry})
            ? $entry 
        : 'foo';
    }
    return $self->{'balance_by'};
}
my $lex = Test->new();
$lex->balance_by('bar');
print $lex->balance_by();
[download]

initially this seemed to work fine, but when I went back and added the line

print $lex->balance_by('baz')
[download]

it still prints "bar". I realize now that the way I used the unless loop makes it impossible to update the value once it has been defined once, but I am at a loss. How should I go about doing this?

thanks in advance,
--au

this was going to be a question about lists, arrays, $_, @_, and shift, but an excellent CB discussion unmuddied my head a bit (or at least showed me that the subject is inherently muddy ;-)