RBXScriptSignal type controls

[Sharksie]

As a developer, when I use RBXScriptSignal I have no control over its type. This is especially problematic when I’m working with custom events from BindableEvents or RemoteEvents. Consumers of these events have to just know what they return. It would be great if these were templates that let me just input what I want as the parameters.

[index_self]

@HugeCoolboy2007

RBXScriptSignal has generics

No, they don’t.

---

Bindables are sort of a discouraged API to use, because in cases like these it is impossible for them to have their type inferred.

Instead, you should use a callback system, which not only guarantees strong typing but also avoids creating two separate callbacks that may cause race conditions.

-- Module
local PlayerData = {
	OnDataLoaded = nil :: (Player: Player) -> ()?
}

local function LoadData()
	local Callback = PlayerData.OnDataLoaded
	
	if Callback then
		for Index, Player in Players:GetPlayers() do
			Callback(Player)
		end
	end
end

-- Consumer
local function OnDataLoaded(Player: Player)
end

PlayerData.OnDataLoaded = OnDataLoaded -- Properly Checked

---

As for Remotes, the types they may return are completely deterministic. You should always type every argument as unknown and do some runtime checking (unless its Server → Client, where you can guarantee the types)

[Sharksie]

@HugeCoolboy2007

RBXScriptSignal has generics you can utilize to give specific type information:

?

[HugeCoolboy2007 (omega)]

I was able to use it fine a while back:

Just ignore my previous replies

[Judgy_Oreo (DisplayName)]

@Sharksie

This is especially problematic when I’m working with custom events from BindableEvents or RemoteEvents

Heads up, they’re kind of working against typing for network callbacks (RemoteEvents and RemoteFunctions) with the unknown type:

luau-lang/rfcs/blob/master/docs/never-and-unknown-types.md

, i.e., unknown has to be narrowed down and is specifically intended for data sent “over the wire”, and it appears to have been enabled with the new type solver (albeit with a bug where the guaranteed parameter is incorrectly unknown and not Player):

New Type Solver [Beta]

Encountered an issue with RemoteFunction callback parameters being unknown [image] Also happens if you define with the syntax remote.OnServerInvoke = function(player, ...) I got curious and tried this on TextChatService as well (OnBubbleAdded & OnIncomingMessage), and the same thing occured, so it’s probably an issue for all classes with callbacks Also, apologies if this has been reported already, I assumed not since searching for “callback” in this topic showed no replies

[DaDude_89 (KasCode)]

I’ve forked stravant’s GoodSignal implementation to support types. There’s a pretty wide range of benefits for using pure-Lua signals rather than RBXScriptSignals, so if you plan to switch to that, you could use this:

GoodSignalFork.lua (7.7 KB)

Example usage:

local GoodSignal = require(path.to.GoodSignal)

-- create the signal, and the public signal with no :Fire method
local privateSignal = GoodSignal.new()
local publicSignal = privateSignal:GetEventOnlySignal() :: GoodSignal.Signal<number, string>

-- connect to the public signal
publicSignal:Connect(function(a, b) -- intellisense: a is a number, b is a string
    print(a, b)
end)

-- fire the signal from both the private and public objects
privateSignal:Fire(2, "wow")

publicSignal._Signal:Fire(3, "This also works")