feat: add support for overriding

state, getters and actions can be overridden for multiple reasons, which are in the docs

docs/guide/generic-stores.md

@@ -206,6 +206,50 @@ function baseStore<T extends Category | Todo>() { // [!code ++]
 }
 ```
 
+## Overriding the generic store
+
+The generic store's properties are passed as optionals when defining the store. This means that we can override them.
+
+This is useful when you want to add a default value to the generic store's state.
+
+```ts
+export const useTodoStore = useStore<TodoStore, BaseStore<Todo>>(
+  'todo',
+  {
+    state: { // [!code ++]
+      all: [ // [!code ++]
+        { id: 1, name: 'First Todo', done: false }, // [!code ++]
+      ], // [!code ++]
+    }, // [!code ++]
+    actions: {
+      remove(id: number) {
+        this.all = this.all.filter(item => item.id !== id)
+      },
+    },
+  },
+  baseStore<Todo>(),
+)
+```
+
+Or when you want to disable a getter or action.
+
+```ts
+export const useTodoStore = useStore<TodoStore, BaseStore<Todo>>(
+  'todo',
+  {
+    getters: { // [!code ++]
+      getName: undefined, // getName no longer shows up in the store // [!code ++]
+    }, // [!code ++]
+    actions: {
+      remove(id: number) {
+        this.all = this.all.filter(item => item.id !== id)
+      },
+    },
+  },
+  baseStore<Todo>(),
+)
+```
+
 That's it!
 
 The generic store can also be split up. See an example here: [Generic Examples](/examples/generic).

playground/src/App.vue

@@ -1,8 +1,7 @@
 <script setup lang="ts">
-import { useCategoryStore, useTodoStore } from './store'
+import { useCategoryStore } from './store'
 
 const category = useCategoryStore()
-const todo = useTodoStore()
 </script>
 
 <template>

playground/src/store.ts

@@ -21,12 +21,16 @@ type CategoryStore = PiniaStore<
 
 const state = createState<CategoryStore, BaseStore<Category>>({
   description: 'This is a category store',
+  all: [
+    { id: 1, name: 'Laptops' },
+  ],
 })
 
 const getters = createGetters<CategoryStore, BaseStore<Category>>({
   getMaxId() {
     return this.all.reduce((max, item) => Math.max(max, item.id), 0)
   },
+  getLength: undefined,
 })
 
 const actions = createActions<CategoryStore, BaseStore<Category>>({
@@ -44,7 +48,6 @@ type BaseStore<T> = PiniaStore<
   {
     getLength(): number
     getName(): string | undefined
-    isDone(): boolean | undefined
   },
   {
     add(item: T): void
@@ -79,25 +82,21 @@ type BaseStore<T> = PiniaStore<
 
 // splitting the generic store too
 
-function baseState<T>() {
+function baseState<T extends Category>() {
   return createState<BaseStore<T>>({
     current: null,
     all: [],
   })
 }
 
-function baseGetters<T extends Category | Todo>() {
+function baseGetters<T extends Category>() {
   return createGetters<BaseStore<T>>({
     getLength() {
       return this.all.length
     },
     getName() {
       return this.current?.name
     },
-    isDone() {
-      if (this.current && 'done' in this.current)
-        return this.current?.done
-    },
   })
 }
 
@@ -109,7 +108,7 @@ function baseActions<T>() {
   })
 }
 
-function baseStore<T extends Category | Todo>() {
+function baseStore<T extends Category>() {
   return defineGenericStore<BaseStore<T>>({
     state: baseState<T>(),
     getters: baseGetters<T>(),
@@ -129,30 +128,45 @@ export const useCategoryStore = useStore<CategoryStore, BaseStore<Category>>(
 
 // TODO: support options (persistedstate, etc.)
 
-interface Todo {
+interface Product {
   id: number
   name: string
-  done: boolean
+  price: number
 }
 
-type TodoStore = PiniaStore<
-  'todo',
-  {},
-  {},
+type BaseStore1<T> = PiniaStore<
+  'base1',
   {
-    remove(id: number): void
+    all: T[]
+  },
+  {
+    getTotal(): number
+    getMaxPrice(): number
   },
-  BaseStore<Todo>
+  {
+    add(item: T): void
+  }
 >
 
-export const useTodoStore = useStore<TodoStore, BaseStore<Todo>>(
-  'todo',
-  {
+function baseStore1<T extends Product>() {
+  return defineGenericStore<BaseStore1<T>>({
+    state: {
+      all: [
+        { id: 1, name: 'Laptop', price: 1000 } as T,
+      ],
+    },
+    getters: {
+      getTotal() {
+        return this.all.reduce((total, item) => total + item.price, 0)
+      },
+      getMaxPrice() {
+        return this.all.reduce((max, item) => Math.max(max, item.price), 0)
+      },
+    },
     actions: {
-      remove(id: number) {
-        this.all = this.all.filter(item => item.id !== id)
+      add(item: T) {
+        this.all.push(item)
       },
     },
-  },
-  baseStore<Todo>(),
-)
+  })
+}

src/generic.ts

@@ -11,7 +11,7 @@ import type { ExtractStore, PiniaActionThis, PiniaGetterThis, StoreThis } from '
 export function createState<
   TStore extends Store, TGenericStore extends Store = Store,
 >(
-  state: Omit<ExtractStore<TStore>['state'], keyof ExtractStore<TGenericStore>['state']>,
+  state: Omit<ExtractStore<TStore>['state'], keyof ExtractStore<TGenericStore>['state']> & Partial<ExtractStore<TGenericStore>['state']>,
 ): ExtractStore<TStore>['state'] {
   return state
 }
@@ -66,6 +66,34 @@ export function defineGenericStore<
 }
 // #endregion defineGenericStore
 
+function filterUndefined<T extends Record<string, any>>(obj: T, undefinedProps: Set<string>): T {
+  const result = Object.keys (obj).reduce ((result, key) => {
+    const value = obj[key]
+    if (value !== undefined) {
+      if (typeof value === 'object' && value !== obj && value !== null) {
+        for (const subKey of Object.keys(value)) {
+          if (value[subKey] === undefined)
+            undefinedProps.add (subKey)
+          else
+            result[key as keyof T] = value
+        }
+      }
+    }
+    return result
+  }, {} as T)
+
+  for (const prop of undefinedProps) {
+    for (const key of Object.keys(result)) {
+      for (const subKey of Object.keys(result[key])) {
+        if (subKey === prop)
+          delete result[key][subKey]
+      }
+    }
+  }
+
+  return result
+}
+
 // #region useStore
 /**
  * Defines a store. Can extend a generic store.
@@ -82,6 +110,11 @@ export function useStore<
   store: StoreThis<TStore, TGenericStore>,
   genericStore: StoreThis<TGenericStore> = {},
 ) {
+  const undefinedProps = new Set<string>()
+
+  store = filterUndefined(store, undefinedProps)
+  genericStore = filterUndefined(genericStore, undefinedProps)
+
   return defineStore(id, {
     state: () => ({
       ...genericStore.state,

src/types.ts

@@ -13,6 +13,9 @@ type PiniaActionsTree = Record<string | number | symbol, (...args: any[]) => any
 export type PiniaGetterThis<TStore extends Store, TGenericStore extends Store = TStore> = {
   [K in keyof Omit<ExtractStore<TStore>['getters'], keyof ExtractStore<TGenericStore>['getters']>]:
   (this: TStore) => ReturnType<ExtractStore<TStore>['getters'][K]>
+} & {
+  [K in keyof Partial<ExtractStore<TGenericStore>['getters']>]:
+  ((this: TStore) => ReturnType<ExtractStore<TGenericStore>['getters'][K]>) | undefined
 }
 // #endregion PiniaGetterThis
 
@@ -24,9 +27,9 @@ export type PiniaGetterThis<TStore extends Store, TGenericStore extends Store =
  */
 export type PiniaActionThis<TStore extends Store, TGenericStore extends Store = TStore> = {
   [K in keyof Omit<ExtractStore<TStore>['actions'], keyof ExtractStore<TGenericStore>['actions']>]:
-  (this: TStore, ...args: Parameters<ExtractStore<TStore>['actions'][K]>)
-  => ReturnType<ExtractStore<TStore>['actions'][K]>
-}
+  ((this: TStore, ...args: Parameters<ExtractStore<TStore>['actions'][K]>)
+  => ReturnType<ExtractStore<TStore>['actions'][K]>) | undefined
+} & Partial<ExtractStore<TGenericStore>['actions']>
 // #endregion PiniaActionThis
 
 // #region StoreThis
@@ -36,7 +39,7 @@ export type PiniaActionThis<TStore extends Store, TGenericStore extends Store =
  * @internal
  */
 export interface StoreThis<TStore extends Store, TGenericStore extends Store = Store> {
-  state?: Omit<ExtractStore<TStore>['state'], keyof ExtractStore<TGenericStore>['state']>
+  state?: Omit<ExtractStore<TStore>['state'], keyof ExtractStore<TGenericStore>['state']> & Partial<ExtractStore<TGenericStore>['state']>
   getters?: PiniaGetterThis<TStore, TGenericStore>
   actions?: PiniaActionThis<TStore, TGenericStore>
 }