"""Base class for Sum subclasses and Product.
Blocks access to many built-in methods.
"""
import inspect
import typing
import weakref
from . import annotations
_T = typing.TypeVar("_T")
def _should_include(name, static):
if name in SHADOWED_ATTRIBUTES and static is None:
return False
if isinstance(static, SumMember):
return False
return True
class ADTConstructor:
"""Base class for ADT Constructor classes."""
__slots__ = ()
def __dir__(self):
return [
attribute
for attribute in super().__dir__()
if _should_include(attribute, inspect.getattr_static(self, attribute))
]
__eq__ = object.__eq__
__ne__ = object.__ne__
__hash__ = object.__hash__
SHADOWED_ATTRIBUTES = {
"__add__",
"__contains__",
"__getitem__",
"__iter__",
"__len__",
"__mul__",
"__rmul__",
"count",
"index",
"__lt__",
"__le__",
"__gt__",
"__ge__",
}
for _attribute in SHADOWED_ATTRIBUTES:
setattr(ADTConstructor, _attribute, None)
class SumMember:
"""Accessor for Sum subclass constructor, only accessible from the base."""
def __init__(self, subcls: type):
self.subcls = subcls
def __get__(self, obj, cls):
if cls is ADT_BASES[self.subcls] and obj is None:
return self.subcls
raise AttributeError("Can only access adt members through base class.")
ADT_BASES: typing.MutableMapping[type, type] = weakref.WeakKeyDictionary()
def make_constructor(_cls, name: str, args: typing.Tuple, subclass_order):
"""Create a subclass of _cls with a constructor generated from args."""
length = len(args)
# pylint: disable=missing-docstring
class Constructor(_cls, ADTConstructor, tuple): # type: ignore
__doc__ = f"""Auto-generated subclass {name} of ADT {_cls.__qualname__}.
Takes {length} argument{'' if length == 1 else 's'}.
"""
__slots__ = ()
def __new__(cls, *args):
if len(args) != length:
raise ValueError
return super().__new__(cls, args)
ADT_BASES[Constructor] = _cls
Constructor.__name__ = name
Constructor.__qualname__ = "{qualname}.{name}".format(
qualname=_cls.__qualname__, name=name
)
setattr(_cls, name, SumMember(Constructor))
subclass_order.append(Constructor)
annotations_ = {f"_{index}": arg for (index, arg) in enumerate(args)}
parameters = [
inspect.Parameter(name, inspect.Parameter.POSITIONAL_ONLY, annotation=arg)
for (name, arg) in annotations_.items()
]
annotations_["return"] = _cls.__qualname__
Constructor.__new__.__signature__ = inspect.Signature( # type: ignore
[inspect.Parameter("cls", inspect.Parameter.POSITIONAL_ONLY)] + parameters,
return_annotation=_cls.__qualname__,
)
Constructor.__new__.__annotations__ = annotations_
def make_constructors(cls: typing.Type[_T]):
"""Return all of the constructors of the given class in definition order."""
subclass_order: typing.List[typing.Type[_T]] = []
for name, args in annotations.sum_args_from_annotations(cls).items():
make_constructor(cls, name, args, subclass_order)
return tuple(subclass_order)
__all__ = ["ADTConstructor", "make_constructor"]
