ch-ch-changes

[Andrei Alexandrescu]

Don wrote:
> Andrei Alexandrescu wrote:
>> 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
> 
> Awesome stuff. Will take some time to adjust my thought processes for this.
> Some minor comments:
> * Is Repeat simply a single-parameter form of Cycle? I can't see any 
> difference between them.

Cycle takes a range and essentially provides a (potentially mutable!) 
way of iterating it. Repeat just gives one element. At the moment that 
element is also mutable, so the difference is moot. I'll consider 
removing Repeat.

> * Uniq docs should at least add one word:  Iterates [[consecutively]] 
> unique elements of the given range.
> * find:
> To find the last element of [[a bidirectional]] haystack satisfying 
> pred, call find!(pred)(retro(haystack)).
> 
> (unless Retro also works for forward ranges, which seems unlikely).

Thanks (and correct).

> * There's no pushHeap. Is it planned?

I plan to do something nicer: make Heap an entity of its own instead of 
a collection of disparate functions. I'm unsure about the name because I 
mean "the computer science heap" as opposed to "the heap for allocating 
memory".


Andrei