FWIW, you can use inline syntax with Sorbet[0], one of the two typecheckers that will work with the RBS format (the other being Steep, which does not have inline syntax).

Here's a full example, complete with a typo, based on the example in the blog post: https://bit.ly/3hMEMSp

Here's a truncated excerpt to get the basic idea across:

    # typed: true

    class Merchant
      extend T::Sig

      sig {returns(String)}
      attr_reader :name

      sig {returns(T::Array[Employee])}
      attr_reader :employees

      sig {params(token: String, name: String).void}
      def initialize(token, name)
        @token = token
        @name = name
      end

    end

Disclaimer, I used Sorbet while I was an employee at Stripe. I found it to be a terrific typechecker. It's also just absurdly fast (most of the time).

[0] https://sorbet.org