Custom type union doesn't collapse after some filtering

  1. What do you want to achieve?
    I wanted to check whether a variable with the custom type I created is the first or the second table.
    I expect the !strict type checker not to return an error.

  2. What is the issue?

  3. What solutions have you tried so far? Did you look for solutions on the Developer Hub?
    From what I searched on the Forum, it adds :: any, but it is hacky and ruins the reason I use a custom type to remember what’s inside of a variable.

The code I provided here would work as expected, but the type checker returns an error, I expected the type to collapse into {hello : "world} if b.hello is true, and collapse into {world : “hello”} when I check if is true.

type a = {hello : "world"} | {world : "hello"}

local b : a = {hello = "world"}

if b.hello then
	-- its the first table
elseif then
	-- its the second table
1 Like

Ok two things. Can I see other scripts and can I get a more “clear” understanding. All I get is that you are coding something to check is something. it’s like weird to read

type BuildingStatBase = {
	MaxHealth: number, -- Building's max health.

type ResourceStorageBuildingStat = BuildingStatBase & {
	MaxGold: number? -- If nil, then the building cannot store any gold.

type ResourceProducerBuildingStat = BuildingStatBase & ResourceStorageBuildingStat & {
	GoldPerHour: number? -- If nil, then the building cannot produce any gold.

type DefensiveBuildingStat = BuildingStatBase & {
	Range: number, -- Range's radius where the building position is the center of the circle.
	DPS: number, -- How much damage it deals in a second, damage per hit will be calculated automatically.
	AttackRate: number, -- (seconds) Attack's frequency; How long the building have to wait until it is able to attack again.	

	TownHall = {
		Description = "The core of your base",
		Levels = {
			{ -- Level 1
				MaxHealth = 5000,
				MaxGold = 25000,
		} :: {ResourceStorageBuildingStat},
	Cannon = {
		Description = "Your only defense",
		Levels = {
			{ -- Level 1
				MaxHealth = 100,
				Range = 5,
				DPS = 10,
				AttackRate = 1,
		} :: {DefensiveBuildingStat}

This is the entire script that I had simplified into that example, I want to check if a building is a ResourceStorage, ResoruceProducer, Defensive, etc. The simplest thing to do is to check if a key in a building’s stat exists. But if have any workarounds will be appreciated.

So you want a script to check if a player has number of a itemand if it has enough it can build something???

The code block I sent earlier returns a table with all the building’s stats, when I want to load a building into the game, I do BuildingStats[buildingName] which returns one of the values in the table, now I do not know what type of building that I am loading, and I need to know since each type of building behaves differently. I hope this would clear things up

I believe you can possibly set up values for each building [put a variable value inside the building’s model] and then if you want to check what it is you can run the script to check every buildings variable in workspace [assuming you put your building in serverstorage]

Yes, very straightforward and intuitive alternative! I thank you for your patience, but hopefully filtering type unions would be possible, I will make this the solution for now until an update :slightly_smiling_face:

Good luck with your game. I bet it’s going to be great :wave:

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