add missing __slots__ to containers and their base classes (#1144) (#1147)

* add missing __slots__ to containers and their base classes (#1144)

* Fix flake8 issue

Author: ariebovenberg

CHANGELOG.md

@@ -5,6 +5,11 @@ Versions before `1.0.0` are `0Ver`-based:
 incremental in minor, bugfixes only are patches.
 See [0Ver](https://0ver.org/).
 
+## 0.17.1
+
+### Bugfixes
+
+- Fixes `__slots__` not being set properly in containers and their base classes
 
 ## 0.17.0
 

returns/context/requires_context.py

@@ -77,6 +77,8 @@ class RequiresContext(
 
     """
 
+    __slots__ = ()
+
     #: This field has an extra 'RequiresContext' just because `mypy` needs it.
     _inner_value: Callable[[RequiresContext, _EnvType], _ReturnType]
 

returns/context/requires_context_future_result.py

@@ -95,6 +95,8 @@ class RequiresContextFutureResult(
 
     """
 
+    __slots__ = ()
+
     #: Inner value of `RequiresContext`
     #: is just a function that returns `FutureResult`.
     #: This field has an extra 'RequiresContext' just because `mypy` needs it.

returns/context/requires_context_ioresult.py

@@ -102,6 +102,8 @@ class RequiresContextIOResult(
 
     """
 
+    __slots__ = ()
+
     #: Inner value of `RequiresContext`
     #: is just a function that returns `IOResult`.
     #: This field has an extra 'RequiresContext' just because `mypy` needs it.

returns/context/requires_context_result.py

@@ -93,6 +93,8 @@ class RequiresContextResult(
 
     """
 
+    __slots__ = ()
+
     #: This field has an extra 'RequiresContext' just because `mypy` needs it.
     _inner_value: Callable[
         [RequiresContextResult, _EnvType],

returns/contrib/pytest/plugin.py

@@ -3,15 +3,14 @@
 from contextlib import contextmanager
 from functools import partial, wraps
 from types import FrameType
-from typing import TYPE_CHECKING, Any, Callable, Iterator, TypeVar, Union
+from typing import TYPE_CHECKING, Any, Callable, Dict, Iterator, TypeVar, Union
 
 import pytest
 from typing_extensions import Final, final
 
 if TYPE_CHECKING:
     from returns.interfaces.specific.result import ResultLikeN
 
-_ERROR_FIELD: Final = '_error_handled'
 _ERROR_HANDLERS: Final = (
     'lash',
 )
@@ -20,6 +19,17 @@
     'alt',
 )
 
+# We keep track of errors handled by keeping a mapping of <object id>: object.
+# If an error is handled, it is in the mapping.
+# If it isn't in the mapping, the error is not handled.
+#
+# Note only storing object IDs would not work, as objects may be GC'ed
+# and their object id assigned to another object.
+# Also, the object itself cannot be (in) the key because
+# (1) we cannot always assume hashability and
+# (2) we need to track the object identity, not its value
+_ERRORS_HANDLED: Final[Dict[int, Any]] = {}  # noqa: WPS407
+
 _FunctionType = TypeVar('_FunctionType', bound=Callable)
 _ReturnsResultType = TypeVar(
     '_ReturnsResultType',
@@ -33,8 +43,8 @@ class ReturnsAsserts(object):
 
     __slots__ = ()
 
-    def assert_equal(
-        self,
+    @staticmethod  # noqa: WPS602
+    def assert_equal(  # noqa: WPS602
         first,
         second,
         *,
@@ -45,13 +55,14 @@ def assert_equal(
         from returns.primitives.asserts import assert_equal
         assert_equal(first, second, deps=deps, backend=backend)
 
-    def is_error_handled(self, container) -> bool:
+    @staticmethod  # noqa: WPS602
+    def is_error_handled(container) -> bool:  # noqa: WPS602
         """Ensures that container has its error handled in the end."""
-        return bool(getattr(container, _ERROR_FIELD, False))
+        return id(container) in _ERRORS_HANDLED
 
+    @staticmethod  # noqa: WPS602
     @contextmanager
-    def assert_trace(
-        self,
+    def assert_trace(  # noqa: WPS602
         trace_type: _ReturnsResultType,
         function_to_search: _FunctionType,
     ) -> Iterator[None]:
@@ -76,11 +87,18 @@ def assert_trace(
 
 
 @pytest.fixture(scope='session')
-def returns(_patch_containers) -> ReturnsAsserts:  # noqa: WPS442
+def returns(_patch_containers) -> ReturnsAsserts:
     """Returns our own class with helpers assertions to check containers."""
     return ReturnsAsserts()
 
 
+@pytest.fixture(autouse=True)
+def _clear_errors_handled():
+    """Ensures the 'errors handled' registry doesn't leak memory."""
+    yield
+    _ERRORS_HANDLED.clear()
+
+
 def pytest_configure(config) -> None:
     """
     Hook to be executed on import.
@@ -182,16 +200,12 @@ def error_handler(cls, original):
         if inspect.iscoroutinefunction(original):
             async def factory(self, *args, **kwargs):
                 original_result = await original(self, *args, **kwargs)
-                object.__setattr__(
-                    original_result, _ERROR_FIELD, True,  # noqa: WPS425
-                )
+                _ERRORS_HANDLED[id(original_result)] = original_result
                 return original_result
         else:
             def factory(self, *args, **kwargs):
                 original_result = original(self, *args, **kwargs)
-                object.__setattr__(
-                    original_result, _ERROR_FIELD, True,  # noqa: WPS425
-                )
+                _ERRORS_HANDLED[id(original_result)] = original_result
                 return original_result
         return wraps(original)(factory)
 
@@ -200,20 +214,14 @@ def copy_handler(cls, original):
         if inspect.iscoroutinefunction(original):
             async def factory(self, *args, **kwargs):
                 original_result = await original(self, *args, **kwargs)
-                object.__setattr__(
-                    original_result,
-                    _ERROR_FIELD,
-                    getattr(self, _ERROR_FIELD, False),
-                )
+                if id(self) in _ERRORS_HANDLED:
+                    _ERRORS_HANDLED[id(original_result)] = original_result
                 return original_result
         else:
             def factory(self, *args, **kwargs):
                 original_result = original(self, *args, **kwargs)
-                object.__setattr__(
-                    original_result,
-                    _ERROR_FIELD,
-                    getattr(self, _ERROR_FIELD, False),
-                )
+                if id(self) in _ERRORS_HANDLED:
+                    _ERRORS_HANDLED[id(original_result)] = original_result
                 return original_result
         return wraps(original)(factory)
 

returns/future.py

@@ -85,6 +85,8 @@ class Future(
 
     """
 
+    __slots__ = ()
+
     _inner_value: Awaitable[_ValueType]
 
     def __init__(self, inner_value: Awaitable[_ValueType]) -> None:
@@ -522,6 +524,8 @@ class FutureResult(
 
     """
 
+    __slots__ = ()
+
     _inner_value: Awaitable[Result[_ValueType, _ErrorType]]
 
     def __init__(

returns/interfaces/altable.py

@@ -35,6 +35,8 @@ class _LawSpec(LawSpecDef):
     https://en.wikibooks.org/wiki/Haskell/The_Functor_class#The_functor_laws
     """
 
+    __slots__ = ()
+
     @law_definition
     def identity_law(
         altable: 'AltableN[_FirstType, _SecondType, _ThirdType]',
@@ -61,6 +63,8 @@ class AltableN(
 ):
     """Modifies the second type argument with a pure function."""
 
+    __slots__ = ()
+
     _laws: ClassVar[Sequence[Law]] = (
         Law1(_LawSpec.identity_law),
         Law3(_LawSpec.associative_law),

returns/interfaces/applicative.py

@@ -37,6 +37,8 @@ class _LawSpec(LawSpecDef):
     Discussion: https://bit.ly/3jffz3L
     """
 
+    __slots__ = ()
+
     @law_definition
     def identity_law(
         container: 'ApplicativeN[_FirstType, _SecondType, _ThirdType]',
@@ -131,6 +133,8 @@ class ApplicativeN(
 
     """
 
+    __slots__ = ()
+
     _laws: ClassVar[Sequence[Law]] = (
         Law1(_LawSpec.identity_law),
         Law3(_LawSpec.interchange_law),

returns/interfaces/bimappable.py

@@ -21,6 +21,8 @@ class BiMappableN(
 
     """
 
+    __slots__ = ()
+
 
 #: Type alias for kinds with two type arguments.
 BiMappable2 = BiMappableN[_FirstType, _SecondType, NoReturn]