package Foo;

use Alter ego => {}; 

my @attr = qw ( bar quux );

sub new {
    my $class = shift;
    my $obj = {}; 
    bless $obj, $class;
    if ( @_) {
        @_ % 2 and die "odd number of arguments, aborted";
        my %args = @_; 
        my %params;
        for (@attr) {
            $params{ $_} = delete $args{ $_};
        }   
        warn "unknown key $_!\n" for keys %args;
        for ( keys %params) {
            $obj->$_( $params{ $_});
        }   
    }   
    return $obj;
}

sub bar {
    my $obj = shift;
    ego( $obj)->{ bar} = shift if @_;
    return ego( $obj)->{ bar}; 
}   

sub quux {
    my $obj = shift;
    ego( $obj)->{ quux} = shift if @_;
    ego( $obj)->{ quux};
}   

package main;

print "\nOutput:\n"

my $foo = Foo->new( foo => 1, bar => 2, quux => 3);

print "\$foo reference is '$foo'\n";

$foo->{bar} = "something"; # hash lookup
$foo->bar(5);              # method

print "method: \$foo->bar( ) = ", $foo->bar( ), "\n";
print "hash:   \$foo->{ bar} = ", $foo->{ bar}, "\n";
__END__

Output:
unknown key foo!
$foo reference is 'Foo=HASH(0x8a007a4)'
method: $foo->bar( ) = 5
hash:   $foo->{ bar} = something