transversal sum

[Artur Skawina via Digitalmars-d-learn]

On 11/06/14 18:32, bearophile via Digitalmars-d-learn wrote:
> Marc Schütz:
> 
>> We'd need something taking and returning a RoR that "mirrors" them diagonally. Then we could simply apply `map!(r => r.sum)` on the result.
> 
> A simple solution is to create a row of values, and then sum them correctly while you scan the rows.

The simplest solution is probably something like:

   auto transversal_sum(FR)(FR rr) {
      static struct TS {
         FR rr;
         bool empty() @property const { return rr.front.empty; }
         auto front() @property {
            import std.algorithm;
            return reduce!((a, b)=>a+b.front)(rr.front.front.init, rr);
         }
         void popFront() { foreach (ref r; rr) r.popFront(); }
      }
      return TS(rr);
   }

but I think OP wanted a ready-made phobos solution, w/o all the
range boilerplate...

artur