Iterating over multiple collections in parallel

[Walter Bright]

Koroskin Denis wrote:
> I spend a lot of time on this and have found no solution how to do it 
> with existing D feature set, but this is surely doable with a few 
> inter-function gotos and an exception if collections sizes don't match. 

It's a well-known problem, and not so easy to solve in an intuitive, 
non-klunky way. Some of the issues are what do you do when the 
collections are of different sizes? Error? Iterate to the minimum? 
Iterate to the maximum and use default values for the shorter collections?

The best I can offer at the moment is:

     foreach (i; 0 .. a.length)
	a[i] = b[i] + c[i];