Cannot use userdata in a .d.lua file?

[davidgiven]

I'm trying to declare a host function which returns a userdata type in my type definition file:

declare function Something(): userdata

This fails with a 'Unknown type: userdata' error.

Is this intentional / something I'm doing wrong / a bug / other?

As an aside: given that userdatas can represent different types of object, is there a way to generate a custom type for userdatas such that different types are not assignable?

type Cat = userdata
type Dog = userdata

local cat: Cat
local dog: Dog
cat = dog -- should produce an error

[JohnnyMorganz]

You can use class types in definition files which can replicate user datas / host types:

declare class Cat
  Name: string
  function Meow(): ()
end