Operator based BaseMetadata creation

[hanjinliu]

Hi all,
I really like the idea of BaseMetadata to formulate Annotated types.

However, configuration using functions such as Gt(10) is not as easy as x > 10 to read. It would be nice to provide a non-constraint class All and support methods such as __gt__ like below.

class All(BaseMetadata):
    def __gt__(self, other):
        return Gt(other)

X = All()  # could be better to keep `All` private and provide `X` publically.
Annotated[int, X > 5]  # equivalent to Annotated[int, Gt(5)]

Similar logic can by applied to construct several objects.

• Interval from 2 < X < 5
• MultipleOf from X % 3 == 0
• MaxLen from X.len() <= 10

[Zac-HD]

Ooh, I really like this idea! It's going to be a little tricky to implement support for chained comparisons and len(X), at least if we want to give good error messages when misused, but worth it for how sweet the syntax will be 🤩

[samuelcolvin]

Awesome idea, thanks @hanjinliu. I'll review the PR now.

[hanjinliu]

Thank you all for the consideration! Looking forward to seeing it.

[Zac-HD]

Per #30, this sadly seems too complex and edge-case-prone to support for now.

Nonetheless, we really appreciate your contribution of design feedback 🙏- thanks!