ch-ch-changes

[Andrei Alexandrescu]

I've worked valiantly on defining the range infrastructure and making 
std.algorithm work with it. I have to say that I'm even more pleased 
with the result than I'd ever expected when I started. Ranges and 
concepts really make for beautiful code, and I am sure pretty darn 
efficient too.

There's a lot to sink one's teeth in, but unfortunately the code hinges 
on a compiler fix that Walter was kind enough to send me privately. I 
did document the work, but the documentation doesn't really make justice 
to the extraordinary possibilities that lay ahead of us. Anyhow, here's 
a sneak preview into the up-and-coming ranges and their algorithms.

http://ssli.ee.washington.edu/~aalexand/d/web/phobos/std_range.html
http://ssli.ee.washington.edu/~aalexand/d/web/phobos/std_algorithm.html

Ranges are easy to define and compose efficiently. It was, however, a 
pig to get a zip(r1, r2, ...) working that can mutate back the ranges it 
iterates on. With that, it's very easy to e.g. sort multiple arrays in 
parallel. Similarly, chain(r1, r2, ...) is able to offer e.g. random 
iteration if all components offer it, which means that you can do crazy 
things like sorting data that sits partially in one array and partially 
in another.

Singly-linked list ranges are in, and to my soothing I found an answer 
to the container/range dichotomy in the form of a topology policy. A 
range may or may not be able to modify the topology of the data it's 
iterating over; if it can, it's a free-standing range, much like 
built-in arrays are. If it can't, it's a limited range tied to a 
container (of which I defined none so far, but give me time) and it's 
only the container that can mess with the topology in controlled ways. 
More on that later.

Feedback welcome.


Andrei