Immutable selector return types

src/immutable.ts

@@ -0,0 +1,38 @@
+/** Imported from Immer to avoid having an implicit dependency in this patch */
+type PrimitiveType = number | string | boolean
+type AtomicObject = Function | Promise<any> | Date | RegExp
+export type IfAvailable<T, Fallback = void> =
+  // fallback if any
+  true | false extends (T extends never ? true : false)
+    ? Fallback // fallback if empty type
+    : keyof T extends never
+    ? Fallback // original type
+    : T
+type WeakReferences = IfAvailable<WeakMap<any, any>> | IfAvailable<WeakSet<any>>
+export type WritableDraft<T> = { -readonly [K in keyof T]: Draft<T[K]> }
+export type Draft<T> = T extends PrimitiveType
+  ? T
+  : T extends AtomicObject
+  ? T
+  : T extends IfAvailable<ReadonlyMap<infer K, infer V>> // Map extends ReadonlyMap
+  ? Map<Draft<K>, Draft<V>>
+  : T extends IfAvailable<ReadonlySet<infer V>> // Set extends ReadonlySet
+  ? Set<Draft<V>>
+  : T extends WeakReferences
+  ? T
+  : T extends object
+  ? WritableDraft<T>
+  : T
+export type Immutable<T> = T extends PrimitiveType
+  ? T
+  : T extends AtomicObject
+  ? T
+  : T extends IfAvailable<ReadonlyMap<infer K, infer V>> // Map extends ReadonlyMap
+  ? ReadonlyMap<Immutable<K>, Immutable<V>>
+  : T extends IfAvailable<ReadonlySet<infer V>> // Set extends ReadonlySet
+  ? ReadonlySet<Immutable<V>>
+  : T extends WeakReferences
+  ? T
+  : T extends object
+  ? { readonly [K in keyof T]: Immutable<T[K]> }
+  : T

src/index.ts

@@ -9,7 +9,8 @@ import type {
   Expand,
   ObjValueTuple,
   Head,
-  Tail
+  Tail,
+  Immutable
 } from './types'
 
 export type {
@@ -171,11 +172,11 @@ export interface CreateSelectorFunction<
   <Selectors extends SelectorArray, Result>(
     ...items: [
       ...Selectors,
-      (...args: SelectorResultArray<Selectors>) => Result
+      (...args: SelectorResultArray<Selectors>) => Immutable<Result>
     ]
   ): OutputSelector<
     Selectors,
-    Result,
+    Immutable<Result>,
     (...args: SelectorResultArray<Selectors>) => Result,
     GetParamsFromSelectors<Selectors>,
     Keys
@@ -191,8 +192,8 @@ export interface CreateSelectorFunction<
     ]
   ): OutputSelector<
     Selectors,
-    Result,
-    ((...args: SelectorResultArray<Selectors>) => Result),
+    Immutable<Result>,
+    (...args: SelectorResultArray<Selectors>) => Result,
     GetParamsFromSelectors<Selectors>,
     Keys
   > &
@@ -201,11 +202,11 @@ export interface CreateSelectorFunction<
   /** Input selectors as a separate array */
   <Selectors extends SelectorArray, Result>(
     selectors: [...Selectors],
-    combiner: (...args: SelectorResultArray<Selectors>) => Result,
+    combiner: (...args: SelectorResultArray<Selectors>) => Immutable<Result>,
     options?: CreateSelectorOptions<MemoizeOptions>
   ): OutputSelector<
     Selectors,
-    Result,
+    Immutable<Result>,
     (...args: SelectorResultArray<Selectors>) => Result,
     GetParamsFromSelectors<Selectors>,
     Keys

src/types.ts

@@ -1,5 +1,6 @@
 import type { MergeParameters } from './versionedTypes'
 export type { MergeParameters } from './versionedTypes'
+export type { Immutable } from './immutable'
 
 /*
  *