So if get the point, there is no easy way to test whether something can be treated as a hash ref (for instance) short of trying to do so. So the best way to test is to try and catch any exceptions that indicate failure.

The alternative is that you use B to ask whether you *really* has a hash reference and overload to ask whether your object of some other type has %{} dereferencing magic. This exposes you to more magic than you want to have to know about.

use B 'svref_2object';
use overload ();

sub bad_idea {
    my $thing = shift @_;

    local $@; # Protect against $@ stomping

    return

      # Is a real hash reference
      eval { svref_2object( $thing )->isa( 'B::HV' ) }

      # Pretends to be a hash reference
      or ( overload::Overloaded( $thing )
            and overload::Method( $thing, '%{}' ) );
}
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