From ce5b645b49e7df23ed88e435b47d40ba10054f40 Mon Sep 17 00:00:00 2001
From: flycloudc <flycloudc@qq.com>
Date: Thu, 3 Jul 2025 10:55:14 +0800
Subject: [PATCH] fix(immut/hashmap): prioritize right values

---
 immut/hashmap/HAMT.mbt      | 24 +++++-------------------
 immut/hashmap/HAMT_test.mbt |  6 +++---
 2 files changed, 8 insertions(+), 22 deletions(-)

diff --git a/immut/hashmap/HAMT.mbt b/immut/hashmap/HAMT.mbt
index 7d1fa5dd3..07206ce49 100644
--- a/immut/hashmap/HAMT.mbt
+++ b/immut/hashmap/HAMT.mbt
@@ -319,23 +319,9 @@ pub fn[K, V] size(self : T[K, V]) -> Int {
 }
 
 ///|
-/// Union two hashmaps
+/// Union two hashmaps, right-hand side element is prioritized
 pub fn[K : Eq + Hash, V] T::union(self : T[K, V], other : T[K, V]) -> T[K, V] {
-  match (self, other) {
-    (_, Empty) => self
-    (Empty, _) => other
-    (_, Leaf(k, v)) => self.add(k, v)
-    (Leaf(k, v), _) =>
-      // right-hand side element is prioritized
-      // like Clojure's merge
-      match other.get(k) {
-        Some(_) => other
-        None => other.add(k, v)
-      }
-    (Branch(sa1), Branch(sa2)) =>
-      Branch(sa1.union(sa2, (m1, m2) => m1.union(m2)))
-    (_, _) => self.iter().fold(init=other, (m, kv) => m.add(kv.0, kv.1))
-  }
+  other.iter().fold(init=self, (m, kv) => m.add(kv.0, kv.1))
 }
 
 ///|
@@ -371,15 +357,15 @@ pub fn[K : Eq + Hash, V] T::union_with(
 }
 
 ///|
-/// Intersect two hashmaps
+/// Intersect two hashmaps, right-hand side element is prioritized
 pub fn[K : Eq + Hash, V] T::intersection(
   self : T[K, V],
   other : T[K, V]
 ) -> T[K, V] {
   self
   .iter()
-  .fold(init=Empty, (m, kv) => if other.get(kv.0) is Some(_) {
-    m.add(kv.0, kv.1)
+  .fold(init=Empty, (m, kv) => if other.get(kv.0) is Some(v2) {
+    m.add(kv.0, v2)
   } else {
     m
   })
diff --git a/immut/hashmap/HAMT_test.mbt b/immut/hashmap/HAMT_test.mbt
index ce0773473..d4af2da6d 100644
--- a/immut/hashmap/HAMT_test.mbt
+++ b/immut/hashmap/HAMT_test.mbt
@@ -548,7 +548,7 @@ test "HAMT::union with collision" {
   let m2 = @hashmap.of([(MyString("b"), 20), (MyString("c"), 3)])
   let u = m1.union(m2)
   assert_eq(u.get(MyString("a")), Some(1))
-  assert_eq(u.get(MyString("b")), Some(2))
+  assert_eq(u.get(MyString("b")), Some(20))
   assert_eq(u.get(MyString("c")), Some(3))
 }
 
@@ -566,7 +566,7 @@ test "HAMT::union all cases" {
   let collision2 = @hashmap.of([(MyString("b"), 20), (MyString("c"), 3)])
   let u2 = collision.union(collision2)
   assert_eq(u2.get(MyString("a")), Some(1))
-  assert_eq(u2.get(MyString("b")), Some(2))
+  assert_eq(u2.get(MyString("b")), Some(20))
   assert_eq(u2.get(MyString("c")), Some(3))
 }
 
@@ -605,7 +605,7 @@ test "HAMT::intersection with branch" {
   let inter = m1.intersection(m2)
   assert_eq(inter.get(1), None)
   assert_eq(inter.get(2), Some(2))
-  assert_eq(inter.get(3), Some(3))
+  assert_eq(inter.get(3), Some(30))
   assert_eq(inter.get(4), None)
 }