From e087f369bfd33613eba6c43aabf324bcebf0c6d3 Mon Sep 17 00:00:00 2001
From: Dmitry Zakharov <dzakh.dev@gmail.com>
Date: Sat, 24 May 2025 18:14:37 +0400
Subject: [PATCH 1/2] Make Stdlib.Dict more performant

---
 lib/es6/Stdlib_Dict.js  | 29 ++++++++++++++++-------------
 lib/js/Stdlib_Dict.js   | 29 ++++++++++++++++-------------
 runtime/Stdlib_Dict.res | 41 +++++++++++++++++++++++++----------------
 3 files changed, 57 insertions(+), 42 deletions(-)

diff --git a/lib/es6/Stdlib_Dict.js b/lib/es6/Stdlib_Dict.js
index 51a70b3144..4e35a26d78 100644
--- a/lib/es6/Stdlib_Dict.js
+++ b/lib/es6/Stdlib_Dict.js
@@ -5,22 +5,25 @@ function $$delete$1(dict, string) {
   delete(dict[string]);
 }
 
-function forEach(dict, f) {
-  Object.values(dict).forEach(value => f(value));
-}
+let forEach = ((dict, f) => {
+    for (var key in dict) {
+      f(dict[key]);
+    }
+  });
 
-function forEachWithKey(dict, f) {
-  Object.keys(dict).forEach(key => f(dict[key], key));
-}
+let forEachWithKey = ((dict, f) => {
+    for (var key in dict) {
+      f(dict[key], key);
+    }
+  });
 
-function mapValues(dict, f) {
-  let target = {};
-  Object.keys(dict).forEach(key => {
-    let value = dict[key];
-    target[key] = f(value);
+let mapValues = ((dict, f) => {
+    var target = {};
+    for (var key in dict) {
+      target[key] = f(dict[key]);
+    }
+    return target;
   });
-  return target;
-}
 
 export {
   $$delete$1 as $$delete,
diff --git a/lib/js/Stdlib_Dict.js b/lib/js/Stdlib_Dict.js
index ecb9c90844..1d59819861 100644
--- a/lib/js/Stdlib_Dict.js
+++ b/lib/js/Stdlib_Dict.js
@@ -5,22 +5,25 @@ function $$delete$1(dict, string) {
   delete(dict[string]);
 }
 
-function forEach(dict, f) {
-  Object.values(dict).forEach(value => f(value));
-}
+let forEach = ((dict, f) => {
+    for (var key in dict) {
+      f(dict[key]);
+    }
+  });
 
-function forEachWithKey(dict, f) {
-  Object.keys(dict).forEach(key => f(dict[key], key));
-}
+let forEachWithKey = ((dict, f) => {
+    for (var key in dict) {
+      f(dict[key], key);
+    }
+  });
 
-function mapValues(dict, f) {
-  let target = {};
-  Object.keys(dict).forEach(key => {
-    let value = dict[key];
-    target[key] = f(value);
+let mapValues = ((dict, f) => {
+    var target = {};
+    for (var key in dict) {
+      target[key] = f(dict[key]);
+    }
+    return target;
   });
-  return target;
-}
 
 exports.$$delete = $$delete$1;
 exports.forEach = forEach;
diff --git a/runtime/Stdlib_Dict.res b/runtime/Stdlib_Dict.res
index 7604962689..0cd2a6bec7 100644
--- a/runtime/Stdlib_Dict.res
+++ b/runtime/Stdlib_Dict.res
@@ -24,22 +24,31 @@ let delete = (dict, string) => {
 
 @val external copy: (@as(json`{}`) _, dict<'a>) => dict<'a> = "Object.assign"
 
-let forEach = (dict, f) => {
-  dict->valuesToArray->Stdlib_Array.forEach(value => f(value))
-}
-
-@inline
-let forEachWithKey = (dict, f) => {
-  dict->keysToArray->Stdlib_Array.forEach(key => f(dict->getUnsafe(key), key))
-}
-
-let mapValues = (dict, f) => {
-  let target = make()
-  dict->forEachWithKey((value, key) => {
-    target->set(key, f(value))
-  })
-  target
-}
+let forEach: (dict<'a>, 'a => unit) => unit = %raw(`
+  (dict, f) => {
+    for (var key in dict) {
+      f(dict[key]);
+    }
+  }
+`)
+
+let forEachWithKey: (dict<'a>, ('a, string) => unit) => unit = %raw(`
+  (dict, f) => {
+    for (var key in dict) {
+      f(dict[key], key);
+    }
+  }
+`)
+
+let mapValues: (dict<'a>, 'a => 'b) => dict<'b> = %raw(`
+  (dict, f) => {
+    var target = {};
+    for (var key in dict) {
+      target[key] = f(dict[key]);
+    }
+    return target;
+  }
+`)
 
 external has: (dict<'a>, string) => bool = "%dict_has"
 

From ccb9b62899fa54aae76d22e70505279b49990aa8 Mon Sep 17 00:00:00 2001
From: Dmitry Zakharov <dzakh.dev@gmail.com>
Date: Sat, 24 May 2025 18:15:58 +0400
Subject: [PATCH 2/2] Add changelog

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4e25a06b4f..5ec52185e3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -30,6 +30,7 @@
 - Improve error messages for JSX type mismatches, passing objects where record is expected, passing array literal where tuple is expected, and more. https://github.com/rescript-lang/rescript/pull/7500
 - Show in error messages when coercion can be used to fix a type mismatch. https://github.com/rescript-lang/rescript/pull/7505
 - Remove deprecated pipe last (|>) syntax. https://github.com/rescript-lang/rescript/pull/7512
+- Make `Dict` iterators more performant. https://github.com/rescript-lang/rescript/pull/7517
 
 # 12.0.0-alpha.13