feat: add OptionalField

src/snakia/field/__init__.py

@@ -4,6 +4,7 @@ from .field import Field
 from .float import FloatField
 from .int import IntField
 from .list import ListField
+from .optional import OptionalField
 from .str import StrField
 
 __all__ = [
@@ -13,5 +14,6 @@ __all__ = [
     "FloatField",
     "IntField",
     "ListField",
+    "OptionalField",
     "StrField",
 ]

src/snakia/field/optional.py

@@ -0,0 +1,28 @@
+from typing import Final, TypeVar
+
+from .field import Field
+
+T = TypeVar("T")
+
+
+class OptionalField(Field[T | None]):
+
+    def __init__(
+        self,
+        field: Field[T],
+        *,
+        none_value: bytes = b"",
+    ) -> None:
+        super().__init__(None)
+        self.none_value: Final = none_value
+        self.field: Final = field
+
+    def serialize(self, value: T | None, /) -> bytes:
+        if value is None:
+            return self.none_value
+        return self.field.serialize(value)
+
+    def deserialize(self, serialized: bytes, /) -> T | None:
+        if serialized == self.none_value:
+            return None
+        return self.field.deserialize(serialized)

src/snakia/field/t.py

@@ -5,6 +5,7 @@ from .field import Field as field
 from .float import FloatField as float
 from .int import IntField as int
 from .list import ListField as list
+from .optional import OptionalField as optional
 from .str import StrField as str
 
 __all__ = [
@@ -14,5 +15,6 @@ __all__ = [
     "float",
     "int",
     "list",
+    "optional",
     "str",
 ]