Re: Run-time Indexing of a Compile-Time Tuple

[John Colvin via Digitalmars-d-learn]

On Tuesday, 12 May 2015 at 09:26:07 UTC, John Colvin wrote:

On Monday, 11 May 2015 at 22:46:00 UTC, Per Nordlöw wrote:

The pattern

           final switch (_index)
           {
               import std.range: empty, front;
               foreach (i, R; Rs)
               {
                   case i:
                       assert(!source[i].empty);
                       return source[i].front;
               }
           }

occurring in roundRobin() and now also in my merge at

https://github.com/nordlow/justd/blob/master/range_ex.d#L604

is nor pretty nor concise.

Is there a better way of indexing a compile time tuple with a run-time index?

It may have to work together with CommonType somehow as is shown in my implementation of merge().

I wrote that code in roundRobin to replace a nightmare string mixin. I can't see any way of getting around it, as there is no meaningful CommonType for a tuple of arbitrary ranges. The body of each case statement needs to know the index at compile-time.

Correction: there are ways around it, but none of them are
improvements.