garray: Add g_ptr_array_steal_index*() functions

These make it easy to steal elements from pointer arrays without having
the array’s GDestroyNotify called on them, similarly to what’s possible
with g_hash_table_steal().

Signed-off-by: Philip Withnall <withnall@endlessm.com>

https://bugzilla.gnome.org/show_bug.cgi?id=795376

3 files changed, 107 insertions, 4 deletions

diff --git a/glib/garray.c b/glib/garray.c
index d8f96db90..914eaee34 100644
--- a/glib/garray.c
+++ b/glib/garray.c
@@ -1194,7 +1194,8 @@ g_ptr_array_set_size  (GPtrArray *array,
 static gpointer
 ptr_array_remove_index (GPtrArray *array,
                         guint      index_,
-                        gboolean   fast)
+                        gboolean   fast,
+                        gboolean   free_element)
 {
   GRealPtrArray *rarray = (GRealPtrArray *) array;
   gpointer result;
@@ -1206,7 +1207,7 @@ ptr_array_remove_index (GPtrArray *array,
 
   result = rarray->pdata[index_];
 
-  if (rarray->element_free_func != NULL)
+  if (rarray->element_free_func != NULL && free_element)
     rarray->element_free_func (rarray->pdata[index_]);
 
   if (index_ != rarray->len - 1 && !fast)
@@ -1240,7 +1241,7 @@ gpointer
 g_ptr_array_remove_index (GPtrArray *array,
                           guint      index_)
 {
-  return ptr_array_remove_index (array, index_, FALSE);
+  return ptr_array_remove_index (array, index_, FALSE, TRUE);
 }
 
 /**
@@ -1262,7 +1263,49 @@ gpointer
 g_ptr_array_remove_index_fast (GPtrArray *array,
                                guint      index_)
 {
-  return ptr_array_remove_index (array, index_, TRUE);
+  return ptr_array_remove_index (array, index_, TRUE, TRUE);
+}
+
+/**
+ * g_ptr_array_steal_index:
+ * @array: a #GPtrArray
+ * @index_: the index of the pointer to steal
+ *
+ * Removes the pointer at the given index from the pointer array.
+ * The following elements are moved down one place. The #GDestroyNotify for
+ * @array is *not* called on the removed element; ownership is transferred to
+ * the caller of this function.
+ *
+ * Returns: (transfer full) (nullable): the pointer which was removed
+ * Since: 2.58
+ */
+gpointer
+g_ptr_array_steal_index (GPtrArray *array,
+                         guint      index_)
+{
+  return ptr_array_remove_index (array, index_, FALSE, FALSE);
+}
+
+/**
+ * g_ptr_array_steal_index_fast:
+ * @array: a #GPtrArray
+ * @index_: the index of the pointer to steal
+ *
+ * Removes the pointer at the given index from the pointer array.
+ * The last element in the array is used to fill in the space, so
+ * this function does not preserve the order of the array. But it
+ * is faster than g_ptr_array_steal_index(). The #GDestroyNotify for @array is
+ * *not* called on the removed element; ownership is transferred to the caller
+ * of this function.
+ *
+ * Returns: (transfer full) (nullable): the pointer which was removed
+ * Since: 2.58
+ */
+gpointer
+g_ptr_array_steal_index_fast (GPtrArray *array,
+                              guint      index_)
+{
+  return ptr_array_remove_index (array, index_, TRUE, FALSE);
 }
 
 /**
diff --git a/glib/garray.h b/glib/garray.h
index 3490f14f0..6c8c2c363 100644
--- a/glib/garray.h
+++ b/glib/garray.h
@@ -154,6 +154,12 @@ gpointer   g_ptr_array_remove_index       (GPtrArray        *array,
 GLIB_AVAILABLE_IN_ALL
 gpointer   g_ptr_array_remove_index_fast  (GPtrArray        *array,
 					   guint             index_);
+GLIB_AVAILABLE_IN_2_58
+gpointer   g_ptr_array_steal_index        (GPtrArray        *array,
+                                           guint             index_);
+GLIB_AVAILABLE_IN_2_58
+gpointer   g_ptr_array_steal_index_fast   (GPtrArray        *array,
+                                           guint             index_);
 GLIB_AVAILABLE_IN_ALL
 gboolean   g_ptr_array_remove             (GPtrArray        *array,
 					   gpointer          data);
diff --git a/glib/tests/array-test.c b/glib/tests/array-test.c
index 64b996fb8..8c0872aef 100644
--- a/glib/tests/array-test.c
+++ b/glib/tests/array-test.c
@@ -659,6 +659,59 @@ pointer_array_find_non_empty (void)
 }
 
 static void
+steal_destroy_notify (gpointer data)
+{
+  guint *counter = data;
+  *counter = *counter + 1;
+}
+
+/* Test that g_ptr_array_steal_index() and g_ptr_array_steal_index_fast() can
+ * remove elements from a pointer array without the #GDestroyNotify being called. */
+static void
+pointer_array_steal (void)
+{
+  guint i1 = 0, i2 = 0, i3 = 0, i4 = 0;
+  gpointer out1, out2;
+  GPtrArray *array = g_ptr_array_new_with_free_func (steal_destroy_notify);
+
+  g_ptr_array_add (array, &i1);
+  g_ptr_array_add (array, &i2);
+  g_ptr_array_add (array, &i3);
+  g_ptr_array_add (array, &i4);
+
+  g_assert_cmpuint (array->len, ==, 4);
+
+  /* Remove a single element. */
+  out1 = g_ptr_array_steal_index (array, 0);
+  g_assert_true (out1 == &i1);
+  g_assert_cmpuint (i1, ==, 0);  /* should not have been destroyed */
+
+  /* Following elements should have been moved down. */
+  g_assert_cmpuint (array->len, ==, 3);
+  g_assert_true (g_ptr_array_index (array, 0) == &i2);
+  g_assert_true (g_ptr_array_index (array, 1) == &i3);
+  g_assert_true (g_ptr_array_index (array, 2) == &i4);
+
+  /* Remove another element, quickly. */
+  out2 = g_ptr_array_steal_index_fast (array, 0);
+  g_assert_true (out2 == &i2);
+  g_assert_cmpuint (i2, ==, 0);  /* should not have been destroyed */
+
+  /* Last element should have been swapped in place. */
+  g_assert_cmpuint (array->len, ==, 2);
+  g_assert_true (g_ptr_array_index (array, 0) == &i4);
+  g_assert_true (g_ptr_array_index (array, 1) == &i3);
+
+  /* Check that destroying the pointer array doesn’t affect the stolen elements. */
+  g_ptr_array_unref (array);
+
+  g_assert_cmpuint (i1, ==, 0);
+  g_assert_cmpuint (i2, ==, 0);
+  g_assert_cmpuint (i3, ==, 1);
+  g_assert_cmpuint (i4, ==, 1);
+}
+
+static void
 byte_array_append (void)
 {
   GByteArray *gbarray;
@@ -970,6 +1023,7 @@ main (int argc, char *argv[])
   g_test_add_func ("/pointerarray/sort-with-data", pointer_array_sort_with_data);
   g_test_add_func ("/pointerarray/find/empty", pointer_array_find_empty);
   g_test_add_func ("/pointerarray/find/non-empty", pointer_array_find_non_empty);
+  g_test_add_func ("/pointerarray/steal", pointer_array_steal);
 
   /* byte arrays */
   g_test_add_func ("/bytearray/append", byte_array_append);