fix inplace to not make a shallow copy (#804)

Author: awni

python/src/array.cpp

@@ -802,7 +802,7 @@ void init_array(py::module_& m) {
           "other"_a)
       .def(
           "__iadd__",
-          [](array& a, const ScalarOrArray v) {
+          [](array& a, const ScalarOrArray v) -> array& {
             a.overwrite_descriptor(add(a, to_array(v, a.dtype())));
             return a;
           },
@@ -821,7 +821,7 @@ void init_array(py::module_& m) {
           "other"_a)
       .def(
           "__isub__",
-          [](array& a, const ScalarOrArray v) {
+          [](array& a, const ScalarOrArray v) -> array& {
             a.overwrite_descriptor(subtract(a, to_array(v, a.dtype())));
             return a;
           },
@@ -840,7 +840,7 @@ void init_array(py::module_& m) {
           "other"_a)
       .def(
           "__imul__",
-          [](array& a, const ScalarOrArray v) {
+          [](array& a, const ScalarOrArray v) -> array& {
             a.overwrite_descriptor(multiply(a, to_array(v, a.dtype())));
             return a;
           },
@@ -859,7 +859,7 @@ void init_array(py::module_& m) {
           "other"_a)
       .def(
           "__itruediv__",
-          [](array& a, const ScalarOrArray v) {
+          [](array& a, const ScalarOrArray v) -> array& {
             if (!is_floating_point(a.dtype())) {
               throw std::invalid_argument(
                   "In place division cannot cast to non-floating point type.");
@@ -894,7 +894,7 @@ void init_array(py::module_& m) {
           "other"_a)
       .def(
           "__ifloordiv__",
-          [](array& a, const ScalarOrArray v) {
+          [](array& a, const ScalarOrArray v) -> array& {
             a.overwrite_descriptor(floor_divide(a, to_array(v, a.dtype())));
             return a;
           },
@@ -914,7 +914,7 @@ void init_array(py::module_& m) {
           "other"_a)
       .def(
           "__imod__",
-          [](array& a, const ScalarOrArray v) {
+          [](array& a, const ScalarOrArray v) -> array& {
             a.overwrite_descriptor(remainder(a, to_array(v, a.dtype())));
             return a;
           },
@@ -980,7 +980,7 @@ void init_array(py::module_& m) {
           "other"_a)
       .def(
           "__imatmul__",
-          [](array& a, array& other) {
+          [](array& a, array& other) -> array& {
             a.overwrite_descriptor(matmul(a, other));
             return a;
           },
@@ -999,7 +999,7 @@ void init_array(py::module_& m) {
           "other"_a)
       .def(
           "__ipow__",
-          [](array& a, const ScalarOrArray v) {
+          [](array& a, const ScalarOrArray v) -> array& {
             a.overwrite_descriptor(power(a, to_array(v, a.dtype())));
             return a;
           },
@@ -1034,7 +1034,7 @@ void init_array(py::module_& m) {
           "other"_a)
       .def(
           "__iand__",
-          [](array& a, const ScalarOrArray v) {
+          [](array& a, const ScalarOrArray v) -> array& {
             auto b = to_array(v, a.dtype());
             if (is_floating_point(a.dtype()) || is_floating_point(b.dtype())) {
               throw std::invalid_argument(
@@ -1065,7 +1065,7 @@ void init_array(py::module_& m) {
           "other"_a)
       .def(
           "__ior__",
-          [](array& a, const ScalarOrArray v) {
+          [](array& a, const ScalarOrArray v) -> array& {
             auto b = to_array(v, a.dtype());
             if (is_floating_point(a.dtype()) || is_floating_point(b.dtype())) {
               throw std::invalid_argument(

python/tests/test_array.py

@@ -1442,6 +1442,21 @@ def test_inplace(self):
         b @= a
         self.assertTrue(mx.array_equal(a, b))
 
+    def test_inplace_preserves_ids(self):
+        a = mx.array([1.0])
+        orig_id = id(a)
+        a += mx.array(2.0)
+        self.assertEqual(id(a), orig_id)
+
+        a[0] = 2.0
+        self.assertEqual(id(a), orig_id)
+
+        a -= mx.array(3.0)
+        self.assertEqual(id(a), orig_id)
+
+        a *= mx.array(3.0)
+        self.assertEqual(id(a), orig_id)
+
     def test_load_from_pickled_np(self):
         a = np.array([1, 2, 3], dtype=np.int32)
         b = pickle.loads(pickle.dumps(a))