Add rebind_keep_modifier

hwtypes/adt_util.py

@@ -2,6 +2,7 @@
 from .bit_vector_abc import AbstractBitVectorMeta, AbstractBitVector
 
 from .util import _issubclass
+from hwtypes.modifiers import get_all_modifiers
 
 def rebind_bitvector(
         adt,
@@ -20,3 +21,18 @@ def rebind_bitvector(
         return new_adt
     else:
         return adt
+
+
+def rebind_keep_modifiers(adt, A, B, rebind_sub_types=False):
+    if A is B or (rebind_sub_types and _issubclass(adt, B)):
+        for mod in get_all_modifiers(A):
+            B = mod(B)
+        return B
+    elif isinstance(adt, BoundMeta):
+        new_adt = adt
+        for field in adt.fields:
+            new_field = rebind_keep_modifiers(field, A, B, rebind_sub_types)
+            new_adt = new_adt.rebind(field, new_field)
+        return new_adt
+    else:
+        return adt

hwtypes/modifiers.py

@@ -93,6 +93,11 @@ def get_unmodified(T):
     else:
         raise TypeError(f'{T} has no modifiers')
 
+def get_all_modifiers(T):
+    if is_modified(T):
+        yield from get_all_modifiers(get_unmodified(T))
+        yield get_modifier(T)
+
 _mod_cache = weakref.WeakValueDictionary()
 # This is a factory for type modifiers.
 def make_modifier(name, cache=False):