use warnings;
use Math::BigInt;
use Math::GMP;

my $v = 9;
my %h = (foo => $v);

for (\%h, [$v], \$v, Math::GMP->new($v), Math::BigInt->new($v), $v) {
  ref($_) ? print ref($_), "\n"
          : print "Not a reference\n";
}

__END__

Outputs:

HASH
ARRAY
SCALAR
Math::GMP
Math::BigInt
not a reference