Improve type checking for state objects

src/InternalTypes.luau

@@ -45,8 +45,8 @@ export type StateObject<T> = Types.StateObject<T> & {
 ]]
 
 -- A state object whose value can be set at any time by the user.
-export type Value<T> = Types.Value<T> & {
-	_value: T
+export type Value<T, S = T> = Types.Value<T, S> & {
+	_value: S
 }
 
 -- A state object whose value is derived from other objects using a callback.

src/State/Value.luau

@@ -35,7 +35,7 @@ function class:set(
 	newValue: unknown,
 	force: boolean?
 )
-	local self = self :: InternalTypes.Value<unknown>
+	local self = self :: InternalTypes.Value<unknown, unknown>
 	local oldValue = self._value
 	if force or not isSimilar(oldValue, newValue) then
 		self._value = newValue
@@ -47,7 +47,7 @@ end
 	Returns the interior value of this state object.
 ]]
 function class:_peek(): unknown
-	local self = self :: InternalTypes.Value<unknown>
+	local self = self :: InternalTypes.Value<unknown, unknown>
 	return self._value
 end
 
@@ -56,7 +56,7 @@ function class:get()
 end
 
 function class:destroy()
-	local self = self :: InternalTypes.Value<unknown>
+	local self = self :: InternalTypes.Value<unknown, unknown>
 	if self.scope == nil then
 		logError("destroyedTwice", nil, "Value")
 	end
@@ -66,7 +66,7 @@ end
 local function Value<T>(
 	scope: Types.Scope<unknown>,
 	initialValue: T
-): Types.Value<T>
+): Types.Value<T, any>
 	if initialValue == nil and (typeof(scope) ~= "table" or (scope[1] == nil and next(scope) ~= nil)) then
 		logError("scopeMissing", nil, "Value", "myScope:Value(initialValue)")
 	end
@@ -76,7 +76,7 @@ local function Value<T>(
 		dependentSet = {},
 		_value = initialValue
 	}, CLASS_METATABLE)
-	local self = (self :: any) :: InternalTypes.Value<T>
+	local self = (self :: any) :: InternalTypes.Value<T, any>
 
 	table.insert(scope, self)
 

src/Types.luau

@@ -87,7 +87,7 @@ export type Dependent = ScopedObject & {
 export type StateObject<T> = Dependency & {
 	type: "State",
 	kind: string,
-	[{}]: T -- unindexable phantom data so StateObject actually contains a T
+	____phantom_peekType: (never) -> T -- phantom data so this contains a T
 }
 
 -- Either a constant value of type T, or a state object containing type T.
@@ -101,14 +101,15 @@ export type Use = <T>(target: CanBeState<T>) -> T
 ]]
 
 -- A state object whose value can be set at any time by the user.
-export type Value<T> = StateObject<T> & {
+export type Value<T, S = T> = StateObject<T> & {
 	kind: "State",
- 	set: (Value<T>, newValue: T, force: boolean?) -> ()
+ 	set: (Value<T, S>, newValue: S, force: boolean?) -> (),
+	 ____phantom_setType: (never) -> S -- phantom data so this contains a T
 }
 export type ValueConstructor = <T>(
 	scope: Scope<unknown>,
 	initialValue: T
-) -> Value<T>
+) -> Value<T, any>
 
 -- A state object whose value is derived from other objects using a callback.
 export type Computed<T> = StateObject<T> & Dependent & {

src/init.luau

@@ -27,7 +27,7 @@ export type StateObject<T> = Types.StateObject<T>
 export type Task = Types.Task
 export type Tween<T> = Types.Tween<T>
 export type Use = Types.Use
-export type Value<T> = Types.Value<T>
+export type Value<T, S = T> = Types.Value<T, S>
 export type Version = Types.Version
 
 -- Down the line, this will be conditional based on whether Fusion is being