fix: derived createStore now returns readonly store

.changeset/old-actors-battle.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/store': patch
+---
+
+derived createStore now returns readonly store

docs/reference/classes/ReadonlyStore.md

@@ -0,0 +1,124 @@
+---
+id: ReadonlyStore
+title: ReadonlyStore
+---
+
+# Class: ReadonlyStore\<T\>
+
+Defined in: [store.ts:31](https://github.com/TanStack/store/blob/main/packages/store/src/store.ts#L31)
+
+## Type Parameters
+
+### T
+
+`T`
+
+## Implements
+
+- `Omit`\<[`Store`](Store.md)\<`T`\>, `"setState"`\>
+
+## Constructors
+
+### Constructor
+
+```ts
+new ReadonlyStore<T>(getValue): ReadonlyStore<T>;
+```
+
+Defined in: [store.ts:33](https://github.com/TanStack/store/blob/main/packages/store/src/store.ts#L33)
+
+#### Parameters
+
+##### getValue
+
+(`prev?`) => `T`
+
+#### Returns
+
+`ReadonlyStore`\<`T`\>
+
+### Constructor
+
+```ts
+new ReadonlyStore<T>(initialValue): ReadonlyStore<T>;
+```
+
+Defined in: [store.ts:34](https://github.com/TanStack/store/blob/main/packages/store/src/store.ts#L34)
+
+#### Parameters
+
+##### initialValue
+
+`T`
+
+#### Returns
+
+`ReadonlyStore`\<`T`\>
+
+## Accessors
+
+### state
+
+#### Get Signature
+
+```ts
+get state(): T;
+```
+
+Defined in: [store.ts:42](https://github.com/TanStack/store/blob/main/packages/store/src/store.ts#L42)
+
+##### Returns
+
+`T`
+
+#### Implementation of
+
+```ts
+Omit.state
+```
+
+## Methods
+
+### get()
+
+```ts
+get(): T;
+```
+
+Defined in: [store.ts:45](https://github.com/TanStack/store/blob/main/packages/store/src/store.ts#L45)
+
+#### Returns
+
+`T`
+
+#### Implementation of
+
+```ts
+Omit.get
+```
+
+***
+
+### subscribe()
+
+```ts
+subscribe(observerOrFn): Subscription;
+```
+
+Defined in: [store.ts:48](https://github.com/TanStack/store/blob/main/packages/store/src/store.ts#L48)
+
+#### Parameters
+
+##### observerOrFn
+
+[`Observer`](../type-aliases/Observer.md)\<`T`\> | (`value`) => `void`
+
+#### Returns
+
+[`Subscription`](../interfaces/Subscription.md)
+
+#### Implementation of
+
+```ts
+Omit.subscribe
+```

docs/reference/functions/createStore.md

@@ -8,10 +8,10 @@ title: createStore
 ## Call Signature
 
 ```ts
-function createStore<T>(getValue): Store<T>;
+function createStore<T>(getValue): ReadonlyStore<T>;
 ```
 
-Defined in: [store.ts:31](https://github.com/TanStack/store/blob/main/packages/store/src/store.ts#L31)
+Defined in: [store.ts:55](https://github.com/TanStack/store/blob/main/packages/store/src/store.ts#L55)
 
 ### Type Parameters
 
@@ -27,15 +27,15 @@ Defined in: [store.ts:31](https://github.com/TanStack/store/blob/main/packages/s
 
 ### Returns
 
-[`Store`](../classes/Store.md)\<`T`\>
+[`ReadonlyStore`](../classes/ReadonlyStore.md)\<`T`\>
 
 ## Call Signature
 
 ```ts
 function createStore<T>(initialValue): Store<T>;
 ```
 
-Defined in: [store.ts:32](https://github.com/TanStack/store/blob/main/packages/store/src/store.ts#L32)
+Defined in: [store.ts:58](https://github.com/TanStack/store/blob/main/packages/store/src/store.ts#L58)
 
 ### Type Parameters
 

docs/reference/index.md

@@ -7,6 +7,7 @@ title: "@tanstack/store"
 
 ## Classes
 
+- [ReadonlyStore](classes/ReadonlyStore.md)
 - [Store](classes/Store.md)
 
 ## Interfaces

packages/store/src/store.ts

@@ -28,11 +28,39 @@ export class Store<T> {
   }
 }
 
-export function createStore<T>(getValue: (prev?: NoInfer<T>) => T): Store<T>
+export class ReadonlyStore<T> implements Omit<Store<T>, 'setState'> {
+  private atom: Atom<T>
+  constructor(getValue: (prev?: NoInfer<T>) => T)
+  constructor(initialValue: T)
+  constructor(valueOrFn: T | ((prev?: T) => T)) {
+    // createAtom has overloads that return ReadonlyAtom<T> for functions and Atom<T> for values
+    // Store always needs Atom<T> for setState, so we assert the return type
+    this.atom = createAtom(
+      valueOrFn as T | ((prev?: NoInfer<T>) => T),
+    ) as Atom<T>
+  }
+  public get state() {
+    return this.atom.get()
+  }
+  public get() {
+    return this.state
+  }
+  public subscribe(
+    observerOrFn: Observer<T> | ((value: T) => void),
+  ): Subscription {
+    return this.atom.subscribe(toObserver(observerOrFn))
+  }
+}
+
+export function createStore<T>(
+  getValue: (prev?: NoInfer<T>) => T,
+): ReadonlyStore<T>
 export function createStore<T>(initialValue: T): Store<T>
-export function createStore<T>(valueOrFn: T | ((prev?: T) => T)): Store<T> {
+export function createStore<T>(
+  valueOrFn: T | ((prev?: T) => T),
+): Store<T> | ReadonlyStore<T> {
   if (typeof valueOrFn === 'function') {
-    return new Store(valueOrFn as (prev?: NoInfer<T>) => T)
+    return new ReadonlyStore(valueOrFn as (prev?: NoInfer<T>) => T)
   }
   return new Store(valueOrFn)
 }

packages/store/tests/derived.test.ts

@@ -1,9 +1,9 @@
 import { afterEach, describe, expect, test, vi } from 'vitest'
 import { batch, createStore } from '../src'
 
-import type { Store } from '../src'
+import type { ReadonlyStore, Store } from '../src'
 
-function viFnSubscribe(subscribable: Store<any>) {
+function viFnSubscribe(subscribable: Store<any> | ReadonlyStore<any>) {
   const fn = vi.fn()
   const cleanup = subscribable.subscribe((s) => fn(s)).unsubscribe
   afterEach(() => {