I wrote a blog post about working on Advent of Code in D. You can read it here:http://jordi.inversethought.com/blog/advent-of-d/
on Day 8, I think the original "verbose" code is better in the end. Mixin at least for me makes it a bit less clear on what exactly is going on. On the other hand the latter version is probably easier to maintain and more copy-paste-error-proof.
