Idiomatic adjacent_difference

[Per Nordlöw via Digitalmars-d-learn]

On Friday, 16 October 2015 at 11:48:19 UTC, Edwin van Leeuwen 
wrote:
> zip(r, r[1..$]).map!((t) => t[1]-t[0]);

And for InputRanges (not requiring random-access):

zip(r, r.dropOne).map!((t) => t[1]-t[0]);