How to actually use reselect's libdef?

The reselect libdef is complex and I’m not sure how to read it.

Does it give you some way to pass in generics when use use createSelector, e.g. the type of your state object that will be passed into the returned function, so Flow can figure out the types of arguments etc? How exactly should I do this? I’ve tried this but it causes hundreds of confusing errors:

createSelector<State>(selector1, selector2, (one, two) => {...})

More generally, if a libdef does provide types that accept generics, and is complex enough to need to be documented, where should this documentation live?

[julienw]

I haven’t tried, but wouldn’t the following work:

Instead of

export const testExplicitSelector = createSelector<State, *, *, *>(
  (state: State) => state.x,
  (x) => x + 1
);

do:

export const testExplicitSelector: State => number = createSelector(
  (state: State) => state.x,
  (x) => x + 1
);

Again I haven’t tried (in our project we still use a quite ancient version of flow), but this looks logical.

[jedwards1211]

@samwgoldman it’s extremely unfortunate that the following annotations on the arguments are no longer sufficient for inferring the type parameters:

export const selectStuff = createSelector(
  ({ foo }: State) => foo,
  ({ bar }: State) => bar,
  (foo: number, bar: string): string => repeat(bar, foo)
)

I find it unacceptable to have to explicitly annotate the parameters in this case. This is the first change that’s made me want to rage-quit flow and migrate to TypeScript instead, but sadly I just have too much flow code to have time to migrate my entire codebase. Are there plans to fix this?