from typing import Union, Literal, Any

from pydantic import BaseModel
from pydantic.dataclasses import dataclass


@dataclass
class SuccessResponse:
    success: Literal[True]


@dataclass
class FailedResponse:
    success: Literal[False]
    failed_reason: str


class SmartUnion:
    def __class_getitem__(cls, item):
        class _Model(BaseModel):
            __root__: Union[item]

            class Config:
                smart_union = True

        def _parse(**kwargs: Any) -> Any:
            return _Model(__root__=kwargs).__root__

        return _parse


Response = SmartUnion[SuccessResponse, FailedResponse]

print(Response(**{"success": True}))
print(Response(**{"success": False, "failed_reason": "failed"}))

SuccessResponse(success=True)
FailedResponse(success=False, failed_reason='failed')

from typing import Literal, Union

from pydantic import parse_obj_as
from pydantic.dataclasses import dataclass


@dataclass
class SuccessResponse:
    success: Literal[True]


@dataclass
class FailedResponse:
    success: Literal[False]
    failed_reason: str


class SmartUnion:
    def __class_getitem__(cls, item):
        return lambda **kwargs: parse_obj_as(Union[item], kwargs)


Response = SmartUnion[SuccessResponse, FailedResponse]

print(Response(**{"success": True}))
print(Response(**{"success": False, "failed_reason": "failed"}))