Make EqualityFn slightly more type-safe.

src/defaultMemoize.ts

@@ -126,7 +126,7 @@ export function createCacheKeyComparator(equalityCheck: EqualityFn) {
 /**
  * @public
  */
-export interface DefaultMemoizeOptions {
+export interface DefaultMemoizeOptions<T = any> {
   /**
    * Used to compare the individual arguments of the provided calculation function.
    *
@@ -142,7 +142,7 @@ export interface DefaultMemoizeOptions {
    * use case, where an update to another field in the original data causes a recalculation
    * due to changed references, but the output is still effectively the same.
    */
-  resultEqualityCheck?: EqualityFn
+  resultEqualityCheck?: EqualityFn<T>
   /**
    * The cache size for the selector. If greater than 1, the selector will use an LRU cache internally.
    *
@@ -167,7 +167,7 @@ export interface DefaultMemoizeOptions {
  */
 export function defaultMemoize<Func extends AnyFunction>(
   func: Func,
-  equalityCheckOrOptions?: EqualityFn | DefaultMemoizeOptions
+  equalityCheckOrOptions?: EqualityFn | DefaultMemoizeOptions<ReturnType<Func>>
 ) {
   const providedOptions =
     typeof equalityCheckOrOptions === 'object'
@@ -191,20 +191,20 @@ export function defaultMemoize<Func extends AnyFunction>(
 
   // we reference arguments instead of spreading them for performance reasons
   function memoized() {
-    let value = cache.get(arguments)
+    let value = cache.get(arguments) as ReturnType<Func>
     if (value === NOT_FOUND) {
       // @ts-ignore
-      value = func.apply(null, arguments)
+      value = func.apply(null, arguments) as ReturnType<Func>
       resultsCount++
 
       if (resultEqualityCheck) {
         const entries = cache.getEntries()
         const matchingEntry = entries.find(entry =>
-          resultEqualityCheck(entry.value, value)
+          resultEqualityCheck(entry.value as ReturnType<Func>, value)
         )
 
         if (matchingEntry) {
-          value = matchingEntry.value
+          value = matchingEntry.value as ReturnType<Func>
           resultsCount--
         }
       }

src/types.ts

@@ -295,7 +295,7 @@ export type Combiner<InputSelectors extends SelectorArray, Result> = Distribute<
  *
  * @public
  */
-export type EqualityFn = (a: any, b: any) => boolean
+export type EqualityFn<T = any> = (a: T, b: T) => boolean
 
 /**
  * The frequency of input stability checks.

src/weakMapMemoize.ts

@@ -72,7 +72,7 @@ function createCacheNode<T>(): CacheNode<T> {
 /**
  * @public
  */
-export interface WeakMapMemoizeOptions {
+export interface WeakMapMemoizeOptions<T = any> {
   /**
    * If provided, used to compare a newly generated output value against previous values in the cache.
    * If a match is found, the old value is returned. This addresses the common
@@ -82,7 +82,7 @@ export interface WeakMapMemoizeOptions {
    * use case, where an update to another field in the original data causes a recalculation
    * due to changed references, but the output is still effectively the same.
    */
-  resultEqualityCheck?: EqualityFn
+  resultEqualityCheck?: EqualityFn<T>
 }
 
 /**
@@ -160,7 +160,7 @@ export interface WeakMapMemoizeOptions {
  */
 export function weakMapMemoize<Func extends AnyFunction>(
   func: Func,
-  options: WeakMapMemoizeOptions = {}
+  options: WeakMapMemoizeOptions<ReturnType<Func>> = {}
 ) {
   let fnNode = createCacheNode()
   const { resultEqualityCheck } = options
@@ -222,7 +222,10 @@ export function weakMapMemoize<Func extends AnyFunction>(
 
     if (resultEqualityCheck) {
       const lastResultValue = lastResult?.deref() ?? lastResult
-      if (lastResultValue != null && resultEqualityCheck(lastResultValue, result)) {
+      if (
+        lastResultValue != null &&
+        resultEqualityCheck(lastResultValue as ReturnType<Func>, result)
+      ) {
         result = lastResultValue
         resultsCount !== 0 && resultsCount--
       }