package Foo;

sub new {
    my $proto = shift || die "Must pass a class or object into new()";
    my $class = ref($proto) || $proto;
    bless {}, $class;
}

##</code><code>##

package Foo;

use Scalar::Utils qw( blessed );

sub new {
    die "Must pass a class or object into new()" unless @_;
    my $proto = shift;
    my $class = blessed($proto) or $proto;

    bless {}, $class;
}