Support pydantic validation & serialization

Fixes #1
Unfortunately, the unique constraint I talked about in the issue
will probably need to be put in a seperate package.

Author: Techcable

pyproject.toml

@@ -15,10 +15,17 @@ requires-python = ">=3.9"
 dependencies = []
 dynamic = ["version"]
 
+[project.optional-dependencies]
+pydantic = [
+    "pydantic~=2.11",
+    # needed for improved get_args
+    'typing_extensions>=4.12; python_version<="3.9"',
+]
+
 [dependency-groups]
 mypy = ["mypy~=1.0", {include-group = "typing"}]
-test = ["pytest~=8.3", "pytest-sugar~=1.0"]
-typing = ["typing-extensions~=4.12"]
+test = ["pytest~=8.3", "pytest-sugar~=1.0", "techcable.orderedset[pydantic]"]
+typing = ["typing-extensions~=4.12", "techcable.orderedset[pydantic]"]
 dev = [{include-group = "mypy"}, {include-group = "test"}]
 
 [project.urls]

src/techcable/orderedset/_orderedset.py

@@ -5,7 +5,9 @@
 from typing import TYPE_CHECKING, Any, Optional, TypeVar, overload
 
 if TYPE_CHECKING:
-    from typing_extensions import Protocol, override
+    from pydantic import GetCoreSchemaHandler
+    from pydantic_core import core_schema
+    from typing_extensions import Protocol, get_args, override
 
     class Comparable(Protocol):
         def __lt__(self, other: Comparable) -> bool:
@@ -17,12 +19,25 @@ def __gt__(self, other: Comparable) -> bool:
         def __eq__(self, other: object) -> bool:
             pass
 
+
 else:
     Comparable = object
 
     def override(v):
         return v
 
+    try:
+        from pydantic_core import core_schema
+    except ImportError:
+        pass
+
+    try:
+        # prefer typing_extensions.get_args for python3.9
+        # needed for pydantic
+        from typing_extensions import get_args
+    except ImportError:
+        from typing import get_args
+
 
 T = TypeVar("T")
 U = TypeVar("U", bound=Comparable)
@@ -203,5 +218,35 @@ def __repr__(self) -> str:
     def __str__(self) -> str:
         return f"{{{', '.join(map(repr, self))}}}"
 
+    @classmethod
+    def __get_pydantic_core_schema__(
+        cls, source_type: Any, handler: GetCoreSchemaHandler
+    ) -> core_schema.CoreSchema:
+        # See here: https://docs.pydantic.dev/latest/concepts/types/#generic-containers
+        instance_schema = core_schema.is_instance_schema(cls)
+
+        args = get_args(source_type)
+        if args:
+            # replace the type and rely on Pydantic to generate the right schema for `Sequence`
+            target_type: type = Sequence[args[0]]  # type: ignore
+            sequence_t_schema = handler.generate_schema(target_type)
+        else:
+            sequence_t_schema = handler.generate_schema(Sequence)
+
+        non_instance_schema = core_schema.no_info_after_validator_function(
+            OrderedSet, sequence_t_schema
+        )
+        return core_schema.union_schema(
+            [
+                instance_schema,
+                non_instance_schema,
+            ],
+            serialization=core_schema.plain_serializer_function_ser_schema(
+                list,  # OrderedSet -> list
+                info_arg=False,
+                return_schema=core_schema.list_schema(),
+            ),
+        )
+
 
 __all__ = ("OrderedSet",)

tests/test_pydantic.py

@@ -0,0 +1,20 @@
+import pydantic
+
+from techcable.orderedset import OrderedSet
+
+
+def test_deser_orderedset() -> None:
+    raw_data = [1, 2, 7, 8, 9, 1]
+    res = pydantic.TypeAdapter(OrderedSet[int]).validate_python(raw_data)
+    assert isinstance(res, OrderedSet)
+    assert res == OrderedSet(raw_data)
+    res = pydantic.TypeAdapter(OrderedSet[int]).validate_json("[1,2,7,8,9,1]")
+    assert res == OrderedSet(raw_data)
+
+
+def test_ser_orderedset() -> None:
+    raw_data = [1, 2, 7, 8, 9, 1]
+    oset = OrderedSet(raw_data)
+    ser = pydantic.TypeAdapter(OrderedSet[int]).dump_python(oset)
+    assert isinstance(ser, list)
+    assert ser == list(OrderedSet(raw_data))