Is there any reason why in can't work with dynamic arrays?

[Adam D. Ruppe]

On Tuesday, 17 September 2019 at 17:43:39 UTC, Brett wrote:
> T[] x;
>
> if (y in x) ...
>
> It just checks to see if y is in between 0 and length.

Most people asking for this want it to check that the *value* y 
is in the array x, which is rejected for requiring a linear 
search.

But your idea could be done quickly, just I expect it would cause 
confusion with the people asking for the other.

I like to just check if y >= 0 && y < x.length which is more 
clear  anyway.