Recursive template problem

[BCS]

Reply to Lars,

> maelp wrote:
> 
>> I think what he looks for is not the actual result since his array of
>> reals isn't const (not known at compile time), and he simply wants
>> the actual *code* to be generated at compile time, so none of your
>> solution will work. I've had similar problems of recursive template
>> construction, so since there are several posts, maybe we'll have some
>> answers.
>> 
> That's right. I am using D for numerical computations, so
> fast-executing code is essential. Therefore, I want to use static
> arrays whenever possible, and instead of having to write
> 
> foreach (real r; v) sum += r;
> 
> or similar, i would like expressions such as
> 
> sum = v[0] + v[1] + ...
> 
> to be created at compile time for arrays of any given length. I was
> kinda hoping templates could provide a solution...
> 
> -Lars
> 

First take a look at the code here, it might give you some ideas:
http://www.dsource.org/projects/scrapple/browser/trunk/bignum/bignum.d

somewhere in there is a hunk of code that generate a tuple like T!(1, 2, 
4, 5, ...)
using a foreach over that will let you get compile time enumeration.

Another point to be made is that if you are reading more than just a few 
numbers you may actually be ahead to use the foreach as its code will be 
much shorter (lower memory usage = better cache usage). As a first guess, 
if the unrolled code is more than a memory page long, loop.