TypeForm: Spelling for a type annotation object at runtime

[davidfstr (David Foster)]

@mikeshardmind

For instance, pydantic and msgspec both can take something which look like Annotated[T, Callable[[T], bool] and return T (No longer wrapped with other metadata, and should no longer be treated as having those annotations attached by runtime analysis)

FWIW, the proposed handling of TypeForm in combination with Annotated[...] is already defined to work that way, stripping out the metadata component:

count: int | str = -1
if ismatch(count, Annotated[int, ValueRange(1, float('inf'))]):
    assert_type(count, int)  # NOT: Annotated[int, ...]
else:
    assert_type(count, int | str)

@mikeshardmind

Additionally, this doesn’t address the other issue with TypeForm[Generic[GenericArgs]],

@mikeshardmind

There’s not always going to be an equivalent way to do this with

TypeForm[Form[...]] as best I can tell (due to restrictions on where parameterized generics are allowed)

One such example of this is that typevariables can’t be bound to parameterized generics. Changing this can’t be done without opening the door to full on higher kinded types […]

Sorry I didn’t understand this bit at all:

• TypeForm[Generic[GenericArgs]] isn’t valid syntax because Generic[...] isn’t a type expression (or an annotation expression for that matter).

• RE “typevariables can’t be bound to parameterized generics” I’d have to see an example to understand what you mean. And how is this limitation on type variables related to TypeForm?