[react-redux] Should redux's Dispatch be covariant in type

[rostero1]

Current definition is

type Dispatch<A: { type: $Subtype<string> }> = DispatchAPI<A>;

Would this be better as

type Dispatch<A: { +type: string }> = DispatchAPI<A>;

It'd still allow for tagged literals

type Action = { type: "fire", payload: string};
const func = (dispatch: Dispatch<Action>) => { ... }

But also allow me to mark the type as read-only:

type ActionType<T: string, P> = { +type: T, +payload: P };
type Action = ActionType<"fire", string> | ActionType<"forget", string>;

Which I couldn't do with the current definition. I don't know the answer, which is why I'm filing this as an issue instead of a PR.

[AndrewSouthpaw]

cc @villesau

[martinschayna]

Still relevant, because of deprecation warning of utility class $Subtype in Flow 0.98+

[villesau]

To be honest, I'm not sure what $Subtype<string> actually even means. Maybe it's fine just to remove the $Subtype?

[AndrewSouthpaw]

Where is this happening? I'm not seeing it in redux or react-redux.

[Brianzchen]

I don't know what the impact of this would be if we changed just one, probably would be better once there's an ability to share types between libdefs