The rfind challenge

[FG]

On 2013-01-15 21:59, Andrei Alexandrescu wrote:
> The generic implementation of before is trivial:
>
> auto before(R)(R theBuck, R stopsHere) {
>    static struct Result {
>      bool empty() { return r1 is r2; }
>      auto ref front() { return r1.front; }
>      void popFront() { r1.popFront; }
>      private R r1, r2;
>    }
>    return Result(theBuck, stopsHere);
> }

I'm scared and would feel safer with:
bool empty() { return r1 is r2 || r1.empty(); }


>
> For random-access ranges:
>
> auto before(R)(R theBuck, R stopsHere) {
>    return theBuck[0 .. theBuck.length - stopsHere.length];
> }

This implies that theBuck._end == stopsHere._end, but why?