class AASM::Core::Invokers::ProcInvoker

def parameters_to_arity
  subject.parameters.inject(0) do |memo, parameter|
    case parameter[0]
    when :key, :keyreq
      # Keyword arguments don't count towards positional arity
    when :rest
      memo = memo > 0 ? -memo : -1
    else
      memo += 1
    end
    memo
  end
end