Without D1-style operator overloads, the `in` operator for classes doesn't make sense

[Dominikus Dittes Scherkl]

On Monday, 6 January 2020 at 10:55:15 UTC, Don wrote:
> So I feel that by introducing this deprecation, we've dropped 
> support for OOP container classes.
I would say: create an issue for that - it's not gone yet, only 
deprecated. So should be revertible without problems.