Parameter storage classes on foreach variables

[Timon Gehr]

On 5/17/24 20:59, Quirin Schroll wrote:
> As of now, `foreach` admits `ref` variables as in `foreach (ref x; xs)`. 
> There, `ref` can be used for two conceptually different things:
> * Avoiding copies
> * Mutating the values in place
> 
> If mutating in place is desired, `ref` is an excellent choice.
> However, if mere copy avoiding is desired, another great option would be 
> `in`.

I contest that `in` is a great option every time mere avoiding of copies 
is desired (because it implies transitive `const`).

In general, extending `foreach` to `in` and `out` makes some sense, but 
`out` is likely to be quite controversial, especially the output range 
lowering. When I think of `foreach`, I think of consuming a range, not 
producing one.