fix: no extra calculation with nested memoized selectors (#92)

* add failing test

* minor tweak

* two test cases

* yaaaay!

* update proxy-compare

* update LICENSE

CHANGELOG.md

@@ -1,6 +1,8 @@
 # Change Log
 
 ## [Unreleased]
+### Changed
+- fix: no extra calculation with nested memoized selectors #92
 
 ## [2.0.4] - 2023-05-06
 ### Changed

LICENSE

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2020-2023 Daishi Kato
+Copyright (c) 2020 Daishi Kato
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

__tests__/issue_91_spec.ts

@@ -0,0 +1,57 @@
+import { memoize } from '../src/index';
+
+describe('no extra calculations (#91)', () => {
+  it('nested memoized selectors with primitive value access', () => {
+    const reduxState = {
+      books: {
+        bookByName: {
+          bookPrice1: 50,
+          bookPrice2: 100,
+        },
+      },
+    };
+    let selectAllBooksCount = 0;
+    const selectAllBooks = memoize((state: typeof reduxState) => {
+      selectAllBooksCount += 1;
+      return Object.values(state.books.bookByName);
+    });
+    const selectSomeBooks = memoize((state: typeof reduxState) => {
+      const someBooks = selectAllBooks(state);
+      return someBooks.filter((price) => price === 100);
+    });
+    const selectBooks = memoize((state: typeof reduxState) => {
+      const allBooks = selectAllBooks(state);
+      const someBooks = selectSomeBooks(state);
+      return { allBooks, someBooks };
+    });
+    selectBooks(reduxState);
+    expect(selectAllBooksCount).toBe(1);
+  });
+
+  it('nested memoized selectors with object access', () => {
+    const reduxState = {
+      books: {
+        bookByName: {
+          book1: { price: 50 },
+          book2: { price: 100 },
+        },
+      },
+    };
+    let selectAllBooksCount = 0;
+    const selectAllBooks = memoize((state: typeof reduxState) => {
+      selectAllBooksCount += 1;
+      return Object.values(state.books.bookByName);
+    });
+    const selectSomeBooks = memoize((state: typeof reduxState) => {
+      const someBooks = selectAllBooks(state);
+      return someBooks.filter((book) => book.price === 100);
+    });
+    const selectBooks = memoize((state: typeof reduxState) => {
+      const allBooks = selectAllBooks(state);
+      const someBooks = selectSomeBooks(state);
+      return { allBooks, someBooks };
+    });
+    selectBooks(reduxState);
+    expect(selectAllBooksCount).toBe(1);
+  });
+});

package.json

@@ -45,7 +45,7 @@
   ],
   "license": "MIT",
   "dependencies": {
-    "proxy-compare": "2.5.1"
+    "proxy-compare": "2.6.0"
   },
   "devDependencies": {
     "@types/jest": "^29.5.1",

src/memoize.ts

@@ -67,6 +67,12 @@ const touchAffected = (dst: unknown, src: unknown, affected: Affected) => {
   });
 };
 
+const isOriginalEqual = (x: unknown, y: unknown): boolean => {
+  for (let xx = x; xx; x = xx, xx = getUntracked(xx));
+  for (let yy = y; yy; y = yy, yy = getUntracked(yy));
+  return Object.is(x, y);
+};
+
 // properties
 const OBJ_PROPERTY = 'o';
 const RESULT_PROPERTY = 'r';
@@ -105,7 +111,13 @@ export function memoize<Obj extends object, Result>(
     for (let i = 0; i < size; i += 1) {
       const memo = memoList[(memoListHead + i) % size];
       if (!memo) break;
-      if (!isChanged(memo[OBJ_PROPERTY], obj, memo[AFFECTED_PROPERTY], new WeakMap())) {
+      if (!isChanged(
+        memo[OBJ_PROPERTY],
+        obj,
+        memo[AFFECTED_PROPERTY],
+        new WeakMap(),
+        isOriginalEqual,
+      )) {
         touchAffected(obj, memo[OBJ_PROPERTY], memo[AFFECTED_PROPERTY]);
         resultCache?.set(obj, memo);
         return memo[RESULT_PROPERTY];