my $type = ref $first;
...
croak("...")
  unless $type eq 'HASH' or (ref($first) and UNIVERSAL::isa($first, 'HASH'))

##</code><code>##

use overload (); # added (), according to ysth's suggestion
use Scalar::Util qw/blessed reftype/;
use Carp;

## call this function as: can_deref_as($ref, $type)

sub can_deref_as {
    my ($thing, $type) = @_;
    
    my %overload = (
        HASH   => '%{}',
        ARRAY  => '@{}',
        SCALAR => '${}',
        GLOB   => '*{}',
        CODE   => '&{}'
    );

    croak "Invalid reference type $type" unless $overload{$type};

    return 0 unless ref $thing;
    return 1 if $type eq reftype $thing;
    return 1 if blessed $thing
            and overload::Method($thing, $overload{$type});
    return 0;
}