transforms: add Enum type

sx/__init__.py

@@ -8,13 +8,13 @@ from .types.data import Data, data
 from .types.num import *
 from .types.struct import StructType, Struct
 from .types.seq import Arr, Tuple
-from .types.transforms import Default, Sized, Ref, Transform, Mapped
+from .types.transforms import Default, Sized, Ref, Transform, Mapped, Enum
 from .types.io import AlignTo, AlignedTo
 
 __all__ = [x.__name__ for x in {
-    parse, dump, sizeof, offsetof, default,
+    parse, dump, sizeof, offsetof, default, to_type,
     Context, Type, Stream, Segment,
-    Wrapper, Default, Sized, Ref, Transform, Mapped,
+    Wrapper, Default, Sized, Ref, Transform, Mapped, Enum,
     AlignTo, AlignedTo,
     Data,
     Int, Bool, Float,

sx/types/transforms.py

@@ -1,6 +1,7 @@
 import os
 import errno
-from typing import Any, Optional as O, Generic as G, Union as U, TypeVar, Callable, Sequence, Mapping
+import enum
+from typing import Any, Optional as O, Generic as G, Union as U, TypeVar, Callable, Sequence, Mapping, Type as Ty
 from ..core.base import Type, Context, PathElement, PossibleDynamic
 from ..core.io import Stream, Segment, Pos
 from ..core.meta import Wrapper
@@ -194,3 +195,17 @@ class Mapped(G[T, V], Transform[T, V]):
             str=str or f'{mapping}[{child}]',
             repr=repr or f'<{__name__}.Mapped({child!r}, {mapping!r})>'
         )
+
+
+E = TypeVar('E', bound=enum.Enum)
+
+class Enum(G[T, E], Transform[T, E]):
+    def __init__(self, enum: Ty[E], child: Type[T]) -> None:
+        super().__init__(child,
+            parse=enum,
+            dump=lambda x: x.value,
+            context=False,
+            str=f'{enum.__name__}({child})',
+            repr=f'{__name__}.Enum({enum!r}, {child!r})',
+        )
+