How to typecheck nested tables?

[Bettleeeeeeee (Bettlee)]

I’m wondering how I can add typings to a nested table, but I’ve looked on the forums and found nothing to my problem. Only solutions to local variables and or functions.

I have the following Lua and I want to typecheck Attachment so that Attach shows up whenever doing ...Attachment:Attach

return {

    Attachment = {

        Attach = function(self, Model: Model, Callback: (Animator: Animator, Animation: Animation) -> (Animator, Animation))
            ...
        end
    }
};

[OniiSamaUwU (UwU)]

1. Explicitly declared:

export type class = {
    someFunction: (self: MyClass, arg: string) -> (),
    nestedTable: {
        nestedFunction: (self: typeof(({} :: MyClass).nestedTable, arg: number) -> ()
    }
}

2. Inferred:

--!strict

local class = {
	Attachment = {}
}

function class.Attachment.Attach(self: typeof(class.Attachment), model: Model): () -- etc.
	
end

-- syntactic sugar for above, however, loses self intellisense
function class.Attachment:Attach(model: Model): () -- etc.
	
end

You unfortunately cannot do the second method all in one table as the table isn’t “resolved” yet.

[Bettleeeeeeee (Bettlee)]

What’s the difference between explicitly and inferred?

[NyrionDev (Nyrion)]

You can nest the typechecking itself:

type callback = (Animator: Animator, Animation: Animation) -> (Animator, Animation)
type f = (self: any, Model: Model, Callback: callback) -> any
type response = {Attachment: {Attach: f}}

[Bettleeeeeeee (Bettlee)]

That seems like it would be a bit messy as well as a redundant part that could just be put in the arguments and such

[OniiSamaUwU (UwU)]

Depends on what you are doing. You are better off doing the second method where the script analysis will return the type of your structured table.

I personally use method 1 for all my classes since I can essentially map out what I want my class to have before coding the functionality, and fine-tune the types without having to resort to this pattern:

Edit: Method 1 is also a great way of “hiding” certain keys from showing up, like internal variables.

[Bettleeeeeeee (Bettlee)]

Alright, I will try the first method and see if I can figure it out