-preview=in might break code

[Ola Fosheim Grøstad]

On Friday, 2 October 2020 at 21:57:06 UTC, Daniel N wrote:
> "Therefore, if more than one reference to the same data is 
> passed to a function, they must all be const."

Impossible to prove at compiletime in the general case.

Way too expensive to check at runtime as well as the aliasing can 
happen deep down in a graph.

So you need to specify it as undefined behaviour.