Fix bugs relating to empty GroupLayers

README.md

@@ -108,8 +108,6 @@ In order to preserve the user's intuitive understanding of "layers higher up in
 
 ### Known bugs and issues (breaking)
 
-- Seg-fault when adding an empty group to another empty group <https://github.com/brainglobe/napari-experimental/issues/12>
-
 ### Development Tasks
 
 - Create a standalone docs site that expands on the implementation details section.

src/napari_experimental/group_layer.py

@@ -74,6 +74,9 @@ class GroupLayer(Group[GroupLayerNode], GroupLayerNode):
         are any such Nodes).
     """
 
+    __next_uid: int = -1
+    _uid: int
+
     @property
     def name(self) -> str:
         """
@@ -98,10 +101,33 @@ def visible(self, value: bool) -> None:
                 item.layer.visible = value
         self._visible = value
 
+    @property
+    def uid(self) -> int:
+        """
+        Unique ID of this instance of GroupLayer.
+        Assigned on instantiation and cannot be overwritten.
+        """
+        return self._uid
+
+    def __eq__(self, other: GroupLayer) -> bool:
+        """
+        GroupLayers are only equal if we are pointing to the same object.
+        """
+        return isinstance(other, GroupLayer) and self.uid == other.uid
+
+    def __hash__(self) -> int:
+        """
+        Since GroupLayers are assigned a unique ID on creation, we can use
+        this value as the hash of a particular instance.
+        """
+        return self._uid
+
     def __init__(
         self,
         *items_to_include: Layer | GroupLayerNode | GroupLayer,
     ):
+        # Assign me a unique uid
+        self._uid = GroupLayer._next_uid()
         # Python seems to understand that since GroupLayerNode inherits from
         # Node, and Group also inherits from Node, that GroupLayerNode
         # "wins".
@@ -137,6 +163,15 @@ def __init__(
         # Default to group being visible
         self._visible = True
 
+    @classmethod
+    def _next_uid(cls) -> int:
+        """
+        Return the next free unique ID that can be assigned to an instance of
+        this class, then increment the counter to the next available index.
+        """
+        cls.__next_uid += 1
+        return cls.__next_uid
+
     @staticmethod
     def _revise_indices_based_on_previous_moves(
         original_index: NestedIndex,