Revert "mark data and error as readonly (#1514)"

This reverts commit af6353c.

infinite/index.ts

@@ -41,7 +41,7 @@ export const infinite = ((<Data, Error, Args extends Arguments>(
 ): SWRInfiniteResponse<Data, Error> => {
   const rerender = useState({})[1]
   const didMountRef = useRef<boolean>(false)
-  const dataRef = useRef<Readonly<Data[]>>()
+  const dataRef = useRef<Data[]>()
 
   const {
     cache,
@@ -168,12 +168,7 @@ export const infinite = ((<Data, Error, Args extends Arguments>(
 
   const mutate = useCallback(
     (
-      data?:
-        | Data[]
-        | Readonly<Data[]>
-        | Promise<Data[]>
-        | Promise<Readonly<Data[]>>
-        | MutatorCallback<Data[]>,
+      data: Data[] | undefined | Promise<Data[]> | MutatorCallback<Data[]>,
       shouldRevalidate = true
     ) => {
       // It is possible that the key is still falsy.
@@ -196,9 +191,7 @@ export const infinite = ((<Data, Error, Args extends Arguments>(
   )
 
   // Function to load pages data from the cache based on the page size.
-  const resolvePagesFromCache = (
-    pageSize: number
-  ): Readonly<Data[]> | undefined => {
+  const resolvePagesFromCache = (pageSize: number): Data[] | undefined => {
     // return an array of page data
     const data: Data[] = []
 

src/types.ts

@@ -1,7 +1,6 @@
 import * as revalidateEvents from './constants/revalidate-events'
 
-type Async<Data> = Data | Promise<Data>
-export type FetcherResponse<Data = unknown> = Async<Data>
+export type FetcherResponse<Data = unknown> = Data | Promise<Data>
 
 export type Fetcher<Data = unknown, SWRKey extends Key = Key> =
   /**
@@ -143,8 +142,8 @@ export type Arguments = string | null | ArgumentsTuple | Record<any, any>
 export type Key = Arguments | (() => Arguments)
 
 export type MutatorCallback<Data = any> = (
-  currentValue?: Readonly<Data>
-) => Async<undefined | Data | Readonly<Data>>
+  currentValue?: Data
+) => Promise<undefined | Data> | undefined | Data
 
 export type Broadcaster<Data = any, Error = any> = (
   cache: Cache<Data>,
@@ -161,35 +160,32 @@ export type State<Data, Error> = {
   isValidating?: boolean
 }
 
-type MutatorData<Data> =
-  | Async<Data>
-  | Async<Readonly<Data>>
-  | MutatorCallback<Data>
-
 export type Mutator<Data = any> = (
   cache: Cache,
   key: Key,
-  data?: MutatorData<Data>,
+  data?: Data | Promise<Data> | MutatorCallback<Data>,
   shouldRevalidate?: boolean
-) => Promise<Readonly<Data> | undefined>
+) => Promise<Data | undefined>
 
 export interface ScopedMutator<Data = any> {
   /** This is used for bound mutator */
-  (key: Key, data?: MutatorData<Data>, shouldRevalidate?: boolean): Promise<
-    Readonly<Data> | undefined
-  >
+  (
+    key: Key,
+    data?: Data | Promise<Data> | MutatorCallback<Data>,
+    shouldRevalidate?: boolean
+  ): Promise<Data | undefined>
   /** This is used for global mutator */
   <T = any>(
     key: Key,
-    data?: MutatorData<T>,
+    data?: T | Promise<T> | MutatorCallback<T>,
     shouldRevalidate?: boolean
-  ): Promise<Readonly<T> | undefined>
+  ): Promise<T | undefined>
 }
 
 export type KeyedMutator<Data> = (
-  data?: MutatorData<Data>,
+  data?: Data | Promise<Data> | MutatorCallback<Data>,
   shouldRevalidate?: boolean
-) => Promise<Readonly<Data> | undefined>
+) => Promise<Data | undefined>
 
 // Public types
 
@@ -200,10 +196,10 @@ export type SWRConfiguration<
 > = Partial<PublicConfiguration<Data, Error, SWRKey>>
 
 export interface SWRResponse<Data, Error> {
-  data?: Readonly<Data>
-  error?: Readonly<Error>
-  isValidating: boolean
+  data?: Data
+  error?: Error
   mutate: KeyedMutator<Data>
+  isValidating: boolean
 }
 
 export type KeyLoader<Args extends Arguments = Arguments> =

test/use-swr-local-mutation.test.tsx

@@ -44,7 +44,7 @@ describe('useSWR - local mutation', () => {
       const { data: state, mutate: setState } = useSWR(`${baseKey}--${key}`, {
         fallbackData
       })
-      return [state, setState] as const
+      return [state, setState]
     }
 
     function Page() {