std.range.iota enhancement: supporting more types (AKA issue 10762)

[Jakob Ovrum]

On Tuesday, 24 December 2013 at 10:38:17 UTC, Francesco Cattoglio 
wrote:
> The range will only be a RA range for types that implement (inc 
> * n) and ((end - begin) / step) (used for lenght computation), 
> otherwise it will be a ForwardRange, because it can't be 
> directional if we can't compute the last element in O(1).

Bidirectionality and random access are separate capabilities; the 
former can be supported without the latter through `--end`, and 
`end == start`, and we should support that. If it causes problems 
when the same range is traversed from both ends, then that is an 
issue with the UDT's operator overloads.