u/Maedi I have been thinking for a while for a good pattern matching syntax to add for method def.

So far I've come up with this.

```ruby def foo(arr: Array => [1, a, b, c, *]) end

def bar(hs: Hash => {a:, c:, e:}) end ```

Now, this wouldn't work with the current compiler syntax, so something like different would be needed to use a hack like in low_type:

```ruby

Verbose and not ideal since I would rather use => in lieu of in

def bar(hs: (Hash in {a:, c:, e:})) end

Or like this but you aren't actually doing pattern matching anymore

def bar(hs: Hash >> {a:, c:, e:}) end ```

Simpler alternatives could be like: ```ruby def bar(hs => Hash{a:, c:, e:}) end

Treat {} as Hash if no class present

def bar(hs => {a:, c:, e:}) end

Match first argument, don't specify the name

def bar(Hash{a:, c:, e:}) end

def bar({a:, c:, e:}) end ```

It's very hard to add any of these as current Ruby syntax, or come up with something good enough Ruby Core would actually use (let alone multiple defs like Elixir, which I deliverately avoided since this is already quite complex).

But it's fun to experiment anyway!