Merge guard and sample methods

[val-o]

Proposal

Provide an ability to transform data from clock and source in guard function.

Use case

Suppose we have a simple authentication flow, with following definitions

type UserName = string;
type Password = string;
type AuthFlowState = { type: 'WaitingUserName' } | WaitingPasswordState | { type: 'Done' };
type WaitingPasswordState = { type: 'WaitingPassword'; username: UserName };
declare const isWatingPassword: (state: AuthFlowState) => state is WaitingPasswordState;

const store$ = createStore<AuthFlowState>({ type: 'WaitingUserName' });

const submitPasswordEvent = createEvent<Password>();
type SubmitPasswordArgs = { password: Password; username: UserName };
const submitPassowrdFx = createEffect<SubmitPasswordArgs, unknown>();

guard({
  clock: submitPasswordEvent,
  source: store$,
  filter: isWatingPassword,
  target: submitPassowrdFx,
});

• The submitPassowrdFx should be called once submitPasswordEvent is fired, but only when AuthFlowState is in the right state
• Then we need to collect username from AuthFlowState and password from submitPasswordEvent params in order to call a submitPassowrdFx effect.

The code snipper above won't compile, due to types mismatch, because we also need to pass password from clock. If we would have a mapping function (like fn in sample), which would be called after filtering, we could easily shape a params expected by target effect

Workaround

We can achieve desired behaviour by combining sample with guard as follows:

sample({
  clock: guard({ clock: submitPasswordEvent, source: store$, filter: isWatingPassword }),
  source: submitPasswordEvent,
  fn: (sourceParams, clockParams): SubmitPasswordArgs => ({
    password: sourceParams,
    username: clockParams.username,
  }),
  target: submitPassowrdFx,
});

[doasync]

https://share.effector.dev/xltBEcdq

[zerobias]

The reason why fn is still missing in guard is purely technical - it is quite difficult to write types for guard, so we have not yet succeeded in implementing this feature

[zerobias]

guard will be merged with the sample in the next minor release. right now I am working on types for this feature