feat: initial commit

src/subscribe.luau

@@ -0,0 +1,46 @@
+local atom = require(script.Parent.atom)
+type Atom<T> = atom.Atom<T>
+
+local reference = require(script.Parent.utils.reference)
+
+local function subscribe<State>(atom: Atom<State>, callback: (state: State, lastState: State) -> ()): (() -> (), () -> ())
+	local pending: thread? = nil
+	local state = atom:get()
+
+	local function emit()
+		local lastState = state
+		state = atom:get()
+		callback(state, lastState)
+	end
+
+	local function update()
+		pending = pending or task.defer(function()
+			pending = nil
+			emit()
+		end)
+	end
+
+	local function flush()
+		if pending then
+			pending = task.cancel(pending)
+			emit()
+		end
+	end
+
+	local function unsubscribe()
+		reference.release(atom)
+		atom.listeners[update] = nil
+
+		if pending then
+			pending = task.cancel(pending)
+		end
+	end
+
+	-- Ensure the atom is held in memory while the subscription is active
+	reference.hold(atom)
+	atom.listeners[update] = true
+
+	return unsubscribe, flush
+end
+
+return subscribe