From 314c1e11dff5e0351698e6f82d4c7b399b72ed34 Mon Sep 17 00:00:00 2001
From: Jake Macdonald <jakemac@google.com>
Date: Tue, 5 Nov 2024 18:06:30 +0000
Subject: [PATCH] use values iterator

---
 pkgs/collection/CHANGELOG.md          |  6 ++----
 pkgs/collection/lib/src/equality.dart | 12 +++++++++---
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/pkgs/collection/CHANGELOG.md b/pkgs/collection/CHANGELOG.md
index ffac9249..b6a9c82b 100644
--- a/pkgs/collection/CHANGELOG.md
+++ b/pkgs/collection/CHANGELOG.md
@@ -2,10 +2,8 @@
 
 - Add `IterableMapEntryExtension` for working on `Map` as a list of pairs, using
   `Map.entries`.
-- Use `entries` and `update` in map equality implementations.
-  - Speeds up all equality checks.
-  - Speeds up implementations for maps with slow lookup, at a slight cost for
-    other implementations.
+- Optimize equality and hash code for maps by using `update` and a `values`
+  iterator to avoid extra lookups.
 
 ## 1.19.1
 
diff --git a/pkgs/collection/lib/src/equality.dart b/pkgs/collection/lib/src/equality.dart
index 28874f8d..4ed1c2a5 100644
--- a/pkgs/collection/lib/src/equality.dart
+++ b/pkgs/collection/lib/src/equality.dart
@@ -325,11 +325,15 @@ class MapEquality<K, V> implements Equality<Map<K, V>> {
     var length = map1.length;
     if (length != map2.length) return false;
     Map<_MapEntry, int> equalElementCounts = HashMap();
-    for (var MapEntry(:key, :value) in map1.entries) {
+    var values1 = map1.values.iterator;
+    for (var key in map1.keys) {
+      var value = (values1..moveNext()).current;
       var entry = _MapEntry(this, key, value);
       equalElementCounts.update(entry, (i) => i + 1, ifAbsent: () => 1);
     }
-    for (var MapEntry(:key, :value) in map2.entries) {
+    final values2 = map2.values.iterator;
+    for (var key in map2.keys) {
+      var value = (values2..moveNext()).current;
       var entry = _MapEntry(this, key, value);
       var count =
           equalElementCounts.update(entry, (i) => i - 1, ifAbsent: () => -1);
@@ -342,7 +346,9 @@ class MapEquality<K, V> implements Equality<Map<K, V>> {
   int hash(Map<K, V>? map) {
     if (map == null) return null.hashCode;
     var hash = 0;
-    for (var MapEntry(:key, :value) in map.entries) {
+    var values = map.values.iterator;
+    for (var key in map.keys) {
+      var value = (values..moveNext()).current;
       var keyHash = _keyEquality.hash(key);
       var valueHash = _valueEquality.hash(value);
       hash = (hash + 3 * keyHash + 7 * valueHash) & _hashMask;