Structure and unstructure generic classes

[zhukovgreen]

It is a feature request.

it would be nice if cattrs would support Generic classes definition, i.e.

T = TypeVar("T")

@attr.dataclass
class A(Generic[T]):
    a: T = attr.ib()

@attr.dataclass
class B:
    a_inst: A[int] = attr.ib()

[zhukovgreen]

Now doing something like this:

# cattrs structure hook
def generic_cls_structure(val, cls):
    """Deserialize the object into generic class.

    Cattrs is not working with generic classes yet.
    https://github.com/Tinche/cattrs/issues/65

    However, in order to be able to deserialize such classes
    the solution assumes the replacing of the attributes with
    generic class (TypeVar) with the subscritped type.

    Current limitations:
    works only with List[~T], Tuple[~T] or ~T
    """
    origin_cls = cls.__origin__
    subscrited_cls = cls.__args__[0]
    new_origin_cls_attribs = {}
    t_map = {list: typing.List, tuple: typing.Tuple}
    for f_name, attrib in attr.fields_dict(origin_cls).items():
        f_name: str
        attrib: attr.Attribute
        _counting_attr_props = dict(
            default=attrib.default,
            validator=attrib.validator,
            repr=attrib.repr,
            cmp=attrib.cmp,
            hash=attrib.hash,
            init=attrib.init,
            converter=attrib.converter,
            metadata=attrib.metadata,
            type=attrib.type,
            kw_only=attrib.kw_only,
        )
        # case with List[~T] or Tuple[~T]
        if (
            hasattr(attrib.type, "__origin__")
            and type(attrib.type.__args__[0]) is typing.TypeVar
        ):
            _counting_attr_props["type"] = t_map[attrib.type.__origin__][
                subscrited_cls
            ]
        # case with ~T
        elif type(attrib.type) is typing.TypeVar:
            _counting_attr_props["type"] = subscrited_cls

        new_origin_cls_attribs[f_name] = _CountingAttr(**_counting_attr_props)

    new_origin_cls = attr.make_class(
        name=origin_cls.__name__, attrs=new_origin_cls_attribs
    )
    return cattr.structure(val, new_origin_cls)

[wakemaster39]

if you can handle a fork, #51 I have been using very heavily now in my production environment. It changes the signature of hooks is the only side effect from 2 vars to 3 but it supports deeply nested generics.

[Tinche]

@zhukovgreen Fixed on master!