1 files changed, 49 insertions, 0 deletions
diff --git a/tools/cru-py/cru/_util/_const.py b/tools/cru-py/cru/_util/_const.py
new file mode 100644
index 0000000..bc02c3a
--- /dev/null
+++ b/tools/cru-py/cru/_util/_const.py
@@ -0,0 +1,49 @@
+from enum import Enum, auto
+from typing import Self, TypeGuard, TypeVar
+
+from ._cru import CRU
+
+_T = TypeVar("_T")
+
+
+class CruConstantBase(Enum):
+    @classmethod
+    def check(cls, v: _T | Self) -> TypeGuard[Self]:
+        return isinstance(v, cls)
+
+    @classmethod
+    def check_not(cls, v: _T | Self) -> TypeGuard[_T]:
+        return not cls.check(v)
+
+    @classmethod
+    def value(cls) -> Self:
+        return cls.VALUE  # type: ignore
+
+
+class CruNotFound(CruConstantBase):
+    VALUE = auto()
+
+
+class CruUseDefault(CruConstantBase):
+    VALUE = auto()
+
+
+class CruDontChange(CruConstantBase):
+    VALUE = auto()
+
+
+class CruNoValue(CruConstantBase):
+    VALUE = auto()
+
+
+class CruPlaceholder(CruConstantBase):
+    VALUE = auto()
+
+
+CRU.add_objects(
+    CruNotFound,
+    CruUseDefault,
+    CruDontChange,
+    CruNoValue,
+    CruPlaceholder,
+)