initial refactor for NamedArray

xarray/core/common.py

@@ -223,7 +223,7 @@ def _get_axis_num(self: Any, dim: Hashable) -> int:
             raise ValueError(f"{dim!r} not found in array dimensions {self.dims!r}")
 
     @property
-    def sizes(self: Any) -> Frozen[Hashable, int]:
+    def sizes(self: Any) -> Mapping[Hashable, int]:
         """Ordered mapping from dimension names to lengths.
 
         Immutable.

xarray/core/groupby.py

@@ -699,7 +699,7 @@ class GroupBy(Generic[T_Xarray]):
 
     _groups: dict[GroupKey, GroupIndex] | None
     _dims: tuple[Hashable, ...] | Frozen[Hashable, int] | None
-    _sizes: Frozen[Hashable, int] | None
+    _sizes: Mapping[Hashable, int] | None
 
     def __init__(
         self,
@@ -746,7 +746,7 @@ def __init__(
         self._sizes = None
 
     @property
-    def sizes(self) -> Frozen[Hashable, int]:
+    def sizes(self) -> Mapping[Hashable, int]:
         """Ordered mapping from dimension names to lengths.
 
         Immutable.

xarray/core/types.py

@@ -106,7 +106,7 @@ def dims(self) -> Frozen[Hashable, int] | tuple[Hashable, ...]:
         ...
 
     @property
-    def sizes(self) -> Frozen[Hashable, int]:
+    def sizes(self) -> Mapping[Hashable, int]:
         ...
 
     @property