Associated literal should narrow type (tagged unions) #643
Description
Summary
When you have union with literal attribute it should be possible to narrow based on this attribute
playground
# tagged.py
from dataclasses import dataclass
from typing import Literal, assert_type
@dataclass
class A:
tag: Literal["A"]
value: int
@dataclass
class B:
tag: Literal["B"]
value: str
type AB = A | B
def test(ab: AB) -> None:
if ab.tag == "A":
assert_type(ab.value, int)$ ty check tagged.py
WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
error[type-assertion-failure]: Argument does not have asserted type `int`
--> tagged.py:22:9
|
20 | def test(ab: AB) -> None:
21 | if ab.tag == "A":
22 | assert_type(ab.value, int)
| ^^^^^^^^^^^^--------^^^^^^
| |
| Inferred type of argument is `int | str`
|
info: `int` and `int | str` are not equivalent types
info: rule `type-assertion-failure` is enabled by default
Found 1 diagnostic
Version
ty 0.0.1-alpha.9