Create readonly method

[igorkamyshev]

Abstract

In some cases, I should forbid store modification by external modules.

For example, when I write userService, I want to encapsulate all modification in this service and provide something like readonly store for the rest of the application.

Example:

// user_service.ts
const $userName = createStore('')
  .on(userNamedChanged, (_, newName) => newName)
  .on(fecthUserNameFx.doneData, (_, fetchedName) => fetchedName)

const userService = { $uerName: readonly($userName) }

export default userService

// other_file_in_the_project.ts

import userService from './user_service'

// It's the rest of the application 🌚

So, here I want to forbid .on calls on userService.$userName and usage userService.$userName as a target in any operators.

Motivation

Encapsulation of write operations is a good way to structure any program. So, I think, we need a way to forbid writes to stores in some cases.

[sergeysova]

Implicit: https://share.effector.dev/TBtJRKG3
Explicit: https://share.effector.dev/j3DMfGDf

By @yumauri

[yumauri]

Those snippets above ↑ are just an idea and possible direction of thought, do not take them directly in you code!

[yumauri]

Also, a bit simpler approach — to check not data, but stack parent node: https://share.effector.dev/Sj5XSbo5

[yumauri]

Lyrical digression:

Following my example snippets, one thought came to my mind:

For now, effector’s graph hasn’t any information about edges. All effector’s graph’s edges are just JavaScript references.

What if! We could add some meta-data to edges? Like color. And inside node’s pipe we could get meta-data of the edge, by which one we’ve got data to process?

Let’s say, by default, all edges has no color. We add one edge, paint it in black, and we can filter data — allow only data, which came by this black edge. All API, used after on the node, will add colorless edges (by default) — and we will just ignore data from those new edges.

Same idea, as in my snippets, but embedded inside effector’s core.

Maybe this edges’ meta-data could be used elsewhere, to solve other cases.

[AlexandrHoroshih]

Looks like, since the deprecation of on on derived store, simple $store.map(v => v) would be enough to create readonly version of any store?

UPD:
Effector doesnt warn or errors if mapped store used as target in sample :(
https://share.effector.dev/V8YVMxXi

[sergeysova]

@zerobias What about to deprecate use ReadonlyStore as target?

[zerobias]

Seems reasonable, would you like to create an issue in effector repo for that case?

[AlexandrHoroshih]

Issue for the case:
effector/effector#563