Bring back foreach int indexes

[Steven Schveighoffer]

On Thursday, 30 November 2023 at 18:26:55 UTC, Johan wrote:
>
> - What about the other integer types?  (uint, short, byte, 
> char?)

Yeah, you can use those too. I think the right answer is to 
ensure the length of the array being iterated can't exceed the 
value range of the type using an assert.

And oh god, I know we have to do `char` because "it's an integer 
too!". `bool` is also, you could do `foreach(bool idx, v; arr)`

> - What if `arr.length >= int.max` ? Does the loop become 
> infinite, or does the loop counter stay `size_t` (not 
> accessible by user) and it is cast to `int` (`idx`) upon every 
> iteration ?

I actually tested this (with `ubyte`, not `int`), and what 
happens is interesting. You only get `length % T.max` (or 
something like that) elements.

For instance I did:

```d
foreach(ubyte idx, v; iota(270).array)
{
     writeln(idx);
}
```

and it printed 0 to 13, and was done.

So clearly it uses `ubyte` as the index for iteration, and also 
somehow converts the length to `ubyte` instead of the other way 
around.

But it doesn't use it exactly, because modifying `idx` doesn't 
change the loop. So I don't see why it uses `ubyte` for the 
actual index instead of `size_t`.

Honestly, maybe the easiest fix here is just to fix the actual 
lowering to be more sensical (I would have expected 270 
iterations with repeated indexes 0 to 13 after going through 255).

-Steve