sub foo (ARRAY $arr) { ... }

##</code><code>##

package Bar;

sub new { bless [], shift }

##</code><code>##

my $bar = Bar->new;

foo( $bar );

##</code><code>##

if ($signature)
{
    if (blessed $x)
    {
        return TRUE if $x->isa( $signature );
    }
    elsif (ref $x)
    {
        return TRUE if ref $x eq $signature;
    }
    else
    {
        die "$x doesn't match $signature\n";
    }
}