lockstep alternative for StoppingPolicy.longest

[Ali Çehreli]

On 09/17/2012 03:00 PM, Andrej Mitrovic wrote:
> I need to iterate through two arrays and do some special comparisons,
> but the arrays are not guaranteed to have the same length. lockstep
> doesn't work with the "longest" policy, e.g.:
>
> int[] a = [1, 2];
> int[] b = [1, 2, 3];
>
> foreach (aa, bb; lockstep(a, b, StoppingPolicy.longest))  // throws
> {
> }
>
> What I would like to have is the ability to set a sentinel value when
> .empty returns true for one of the arrays, this would enable this
> policy to work. For example I could have:
>
> foreach (aa, bb; lockstep(a, b, StoppingPolicy.longest, -1))  // sentinel is -1
> {
>      // if aa or bb doesn't exist it's set to -1
> }
>
> or alternatively aa/bb could be pointers, and the sentinel would
> conveniently be null. Is anything like this in Phobos already?

I think you actually want .shortest, no? lockstep's cousin zip() and 
until() may help:

import std.stdio;
import std.range;
import std.algorithm;

void main()
{
     int i, j, k, l, m;
     int*[] a = [&i, null, &j];
     int*[] b = [&k, &l, &m];

     foreach (aa, bb;
              zip(StoppingPolicy.shortest, until!(x => x is null)(a), b))
     {
         writefln("%s and %s", aa, bb);
     }
}

Ali