Selector does not have a generic `set` variant

In the following pattern, there is a selector which serves as the public interface to an underlying private atom. In this situation, it is desirable for the setter to have the ability to accept parameters of a different type than the base value of the selector.

I would like to propose adding a second type parameter to selector, which serves as the type of the accepted parameter to the setter. This would have a default value of selector<T, TSetter = T>. This addition of TSetter will need to propagate up throughout Recoil to ensure all usages remain properly typed.

I will submit a quick barebones PR to demonstrate the gist of it. If this is a pattern you would like to support I can try to introduce it fully and add to the flow typings as well. Thanks!

No functionality change, only adding typings. Contrived example.

class UIStore {
  private _appName = "Hello, World!";
  private _title = atom<string | null>({
    key: "UIStore__Title",
    default: null,
  });

  title = selector<string, string | null>({
    key: "UIStore_Title",
    get: ({ get }) => {
      const title = get(this._title);
      if (title === null) return this._appName;
      else return `${title} | ${this._appName}`;
    },
    set: ({ set, get }, newValue) => {
      let title = newValue;
      if (title === "") title = null;
      set(this._title, title);
    },
  });
}

[adrianbw]

Here’s an example of something else that doesn’t work, which I think maybe you were saying above:

export const exportQueueState = selector<string[]>({
  key: `${namespace}.exportQueue`,
  get: ({ get }): string[] => {
    return get(ExportWatcherStore).exportQueue;
  },
  set: ({ set }, newValue) =>
    set(ExportWatcherStore, (oldState) => ({
      ...oldState,
      exportQueue: oldState.exportQueue.push(newValue), // Argument of type 'string[] | DefaultValue' is not assignable to parameter of type 'string'.
    })),
});

[sanonz]

I released a recoil-types package as a temporary replacement.

npm i recoil-types

Add the following path to the tsconfig.json file.

{
  "compilerOptions": {
    "paths": {
      "recoil": ["node_modules/recoil-types/index"]
    }
  }
}

After the official fix, remove the path and uninstall package recoil-types.