add Swap and CompareAndSwap APIs

Author: alphadose

e2e_test.go

@@ -308,3 +308,47 @@ func TestInfiniteLoop(t *testing.T) {
 		}
 	})
 }
+
+// https://github.com/alphadose/haxmap/issues/18
+// test compare and swap
+func TestCAS(t *testing.T) {
+	type custom struct {
+		val int
+	}
+	m := New[string, custom]()
+	m.Set("1", custom{val: 1})
+	if m.CompareAndSwap("1", custom{val: 420}, custom{val: 2}) {
+		t.Error("Invalid Compare and Swap")
+	}
+	if !m.CompareAndSwap("1", custom{val: 1}, custom{val: 2}) {
+		t.Error("Compare and Swap Failed")
+	}
+	val, ok := m.Get("1")
+	if !ok {
+		t.Error("Key doesnt exists")
+	}
+	if val.val != 2 {
+		t.Error("Invalid Compare and Swap value returned")
+	}
+}
+
+// https://github.com/alphadose/haxmap/issues/18
+// test swap
+func TestSwap(t *testing.T) {
+	m := New[string, int]()
+	m.Set("1", 1)
+	val, swapped := m.Swap("1", 2)
+	if !swapped {
+		t.Error("Swap failed")
+	}
+	if val != 1 {
+		t.Error("Old value not returned in swal")
+	}
+	val, ok := m.Get("1")
+	if !ok {
+		t.Error("Key doesnt exists")
+	}
+	if val != 2 {
+		t.Error("New value not set")
+	}
+}

map.go

@@ -229,6 +229,43 @@ func (m *Map[K, V]) GetOrSet(key K, value V) (actual V, loaded bool) {
 	return
 }
 
+// CompareAndSwap atomically updates a map entry given its key by comparing current value to `oldValue`
+// and setting it to `newValue` if the above comparison is successful
+// It returns a boolean indicating whether the CompareAndSwap was successful or not
+func (m *Map[K, V]) CompareAndSwap(key K, oldValue, newValue V) bool {
+	var (
+		h        = m.hasher(key)
+		existing = m.metadata.Load().indexElement(h)
+	)
+	if existing == nil || existing.keyHash > h {
+		existing = m.listHead
+	}
+	if _, current, _ := existing.search(h, key); current != nil {
+		if oldPtr := current.value.Load(); reflect.DeepEqual(*oldPtr, oldValue) {
+			return current.value.CompareAndSwap(oldPtr, &newValue)
+		}
+	}
+	return false
+}
+
+// Swap atomically swaps the value of a map entry given its key
+// It returns the old value if swap was successful and a boolean `swapped` indicating whether the swap was successful or not
+func (m *Map[K, V]) Swap(key K, newValue V) (oldValue V, swapped bool) {
+	var (
+		h        = m.hasher(key)
+		existing = m.metadata.Load().indexElement(h)
+	)
+	if existing == nil || existing.keyHash > h {
+		existing = m.listHead
+	}
+	if _, current, _ := existing.search(h, key); current != nil {
+		oldValue, swapped = *current.value.Swap(&newValue), true
+	} else {
+		swapped = false
+	}
+	return
+}
+
 // ForEach iterates over key-value pairs and executes the lambda provided for each such pair
 // lambda must return `true` to continue iteration and `false` to break iteration
 func (m *Map[K, V]) ForEach(lambda func(K, V) bool) {