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Alternative way to make appMachine spawned children type safe #5890

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Merged
franknoirot merged 4 commits into from
Apr 4, 2025
Merged

Alternative way to make appMachine spawned children type safe #5890

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2aaf82f
Alternative way to make appMachine spawned children type safe
farskid Mar 19, 2025
69c3e3f
Merge branch 'main' into farskid/appMachine-type-safety
franknoirot Mar 24, 2025
e9ce87a
Add gotcha comments on coercion
franknoirot Apr 3, 2025
a70b719
Merge branch 'main' into farskid/appMachine-type-safety
franknoirot Apr 3, 2025
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26 changes: 18 additions & 8 deletions src/machines/appMachine.ts
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Original file line number Diff line number Diff line change
@@ -1,5 +1,4 @@
import { useSelector } from '@xstate/react'
import type { ActorRefFrom } from 'xstate'
import { createActor, setup, spawnChild } from 'xstate'

import { createSettings } from '@src/lib/settings/initialSettings'
Expand All @@ -14,9 +13,14 @@ const appMachineActors = {
} as const

const appMachine = setup({
types: {} as {
children: {
auth: typeof AUTH
settings: typeof SETTINGS
}
},
actors: appMachineActors,
}).createMachine({
/** @xstate-layout N4IgpgJg5mDOIC5gF8A0IB2B7CdGgAoBbAQwGMALASwzAEp8QAHLWKgFyqw0YA9EAjACZ0AT0FDkU5EA */
id: 'modeling-app',
entry: [
spawnChild(AUTH, { id: AUTH, systemId: AUTH }),
Expand All @@ -29,18 +33,24 @@ const appMachine = setup({
})

export const appActor = createActor(appMachine)
export const authActor = appActor.system.get(AUTH) as ActorRefFrom<
typeof authMachine
>
/**
* GOTCHA: the type coercion of this actor works because it is spawned for
* the lifetime of {appActor}, but would not work if it were invoked
* or if it were destroyed under any conditions during {appActor}'s life
*/
export const authActor = appActor.getSnapshot().children.auth!
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@farskid farskid Mar 19, 2025 •
edited
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Casting is safe here because, when the state snapshot is available, appMachine will have already initialized all spawned children.

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@franknoirot franknoirot Mar 24, 2025

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Nice. If these were invoked actors we'd have to be more cautious with the cast here, or if they were spawned in a more ephemeral way? I just want us to remember that if we make use of other patterns as we break apart the modeling machine, for example.

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@farskid farskid Mar 24, 2025

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Yes, if they were invoked, they'd legitimately be available partially depending on the state. Even spawned actors can be partially unavailable too. It's safe here because we have child actors that are spawned in the root state in the entry action meaning it's the first action that runs before the the first state transition happens in the machine so in other words, these spawns are always available.

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@franknoirot franknoirot Apr 3, 2025

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Thanks, I added a "gotcha" comment here

export const useAuthState = () => useSelector(authActor, (state) => state)
export const useToken = () =>
useSelector(authActor, (state) => state.context.token)
export const useUser = () =>
useSelector(authActor, (state) => state.context.user)

export const settingsActor = appActor.system.get(SETTINGS) as ActorRefFrom<
typeof settingsMachine
>
/**
* GOTCHA: the type coercion of this actor works because it is spawned for
* the lifetime of {appActor}, but would not work if it were invoked
* or if it were destroyed under any conditions during {appActor}'s life
*/
export const settingsActor = appActor.getSnapshot().children.settings!
export const getSettings = () => {
const { currentProject: _, ...settings } = settingsActor.getSnapshot().context
return settings
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