dip1000 and preview in combine to cause extra safety errors

[Dukc]

On Wednesday, 8 June 2022 at 14:52:53 UTC, Steven Schveighoffer 
wrote:
> ```d
> string foo(in string s)
> {
>     return s;
> }
>
> void main()
> {
>     import std.stdio;
>     string[] result;
>     foreach(c; "hello")
>     {
>         result ~= foo([c]);
>     }
>     writeln(result);
> }
> ```
>
> Thoughts?

This is simply the result of using `in` wrong. `in` means `const 
scope`. `scope` (without preceeding `return`) means you won't 
return a reference to the address to the argument (unless the 
function can reach it via some other channel). Result: undefined 
behaviour.