Proposal for SentinelInputRange

[deadalnix]

On Friday, 1 March 2013 at 06:19:19 UTC, Chris Nicholson-Sauls 
wrote:
> A use case that comes immediately to mind: a sentinal range 
> that, yes wraps, an infinite (but predictable!) range, 
> effectively allowing you to take a head-slice of the infinite 
> range.
>
> auto foo = infiniteRangeOfEvenNumbers();
> auto upto1000 = GenericSentinalInputRange!1000( foo );
>

struct GenericSentinelRange(R, Sentinel) {
     R r;

     @property auto front() {
         return r.front;
     }

     void popFront() {
         r.popFront();
     }

     @property empty() {
         return r.front == Sentinel;
     }
}

We don't need a new type of range at all. You confuse legitimate 
uses case for using a sentinel to terminate a range and uses case 
where an actual sentinel range is needed.

> So... I could live without a standard sentinal range concept 
> (have so far, using sentinal injection with input ranges, which 
> as Walter pointed out is really an incorrect use (abuse?) of 
> input ranges), but I also know I'd be using it if it existed 
> (and thereby cleaning up some code versus how I do it now).

You can live without, and guess what : if you use LDC (and 
probably GDC) you'll get the performance boost Walter is talking 
about.