I'm not a OO expert (in what I'm expert? ;) but I almost always start with something like (perl 5.14 5.10 (see below GrandFather's answer) required to use //= ):

sub new{
    my $class = shift;

    my %conf = validate_conf( @_ );

    return bless {
                %conf
    }, $class;
}


sub validate_conf{
    my %conf = @_;
    
    $conf{ map_colors } //= 16;
    $conf{ map_area_w } //= 50; 
    $conf{ map_area_h } //=  20; 
    
    # more logic if needed..
    return %conf;
    
}
[download]

So the fourth option for me

HtH

L*