Yes, it's possible. But it depends on what you actually want to do. If you just want to do what you show in your example, then

my %h=@_;  # is enough!
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But if you also want to modify the hash you pass in, or if you want to pass a few params of which one (or more) happens (happen) to be a hash, then as others already pointed out, you have to use a reference. You can also use a prototype, as explained in perldoc perlsub to have perl doing this for you. But regard that as a somewhat advanced technique and be sure to have understood the docs if you want to apply it...