Intended behavior of std.range.cycle?

[monarch_dodra via Digitalmars-d-learn]

On Thursday, 4 September 2014 at 11:29:30 UTC, rcor wrote:
> auto c = cycle([1,2,3]);
> foreach(i ; iota(-4,4)) {
>   writeln(c[i]);
> }
>
> prints the sequence
> 1
> 2
> 3
> 1
> 1   <----- c[0] == c[-1]
> 2
> 3
>
> I understand this is what would happen if I were to just use 
> modulus on an index to access the original array, but should 
> Cycle really mimic this behavior? I feel like most uses of 
> Cycle would expect element -1 to be the last element of the 
> original range, not the first. I could manually apply addition 
> with modulus to ensure that the index is always positive, but 
> then there's not much benefit to using cycle anyways -- I might 
> as well be accessing the original range.
> Is this behavior intentional or an oversight?

Indexing is done with the unsigned size_t. You aren't indexing at 
"-1", but rather, size_t.max. size_t.max % 3 probably doesn't 
result in "3 - 1" hence what you are observing.

*Should* cycle be negatively index-able? Personally, I don't 
think so. And even if it could, it has been proven non-size_t 
indexing is not well supported at all. It was de-facto chosen 
after the "iota-map fiasco" that all ranges be indexed with 
size_t and nothing else...