Passing $ as a function argument

[lngns]

On Wednesday, 10 October 2018 at 13:32:15 UTC, Simen Kjærås wrote:
> struct Sentinel {}
> Sentinel $;
>
> void foo(T)(T loc) {
>     auto bar = double[RandomPInt+1];
>     static if (is(T == Sentinel)) {
>         return bar[$];
>     } else {
>         return bar[loc];
>     }
> }
>
> unittest {
>     foo($);
> }

It looks to me OP is proposing exactly this, but wants the 
subscript expression to support it.
That would require introducing a new type or changing size_t, so 
that both integer indices and the sentinel can be passed around.
Present-day size_t is unsigned, so we can't use negative values 
to represent it.

I guess it could be useful when you are manipulating multiple 
arrays at the same time in a functional fashion and need the 
upper bound of all of them at one point, which could be different.