Multidimensional foreach

[Simen kjaeraas]

On Fri, 18 Dec 2009 19:49:31 +0100, Bill Baxter <wbaxter at gmail.com> wrote:

> On Fri, Dec 18, 2009 at 5:17 AM, Simen kjaeraas <simen.kjaras at gmail.com>  
> wrote:
>> Simen kjaeraas <simen.kjaras at gmail.com> wrote:
>>
>>> I have a function that returns an N-dimensional array, where N is a
>>> template parameter. Now I want to run a foreach loop through each
>>> element of this array. Is there a known and tested way to do this,
>>> or should I write my own templates to do it?
>>
>> I wrote this implementation. Now, to get some meaningful indices
>> out of it. Do D2's ranges even support that? Oh, and I probably
>> need to rewrite it in terms of an index instead of slices to get
>> that working. Bah.
>>
>> Ideas? Comments? Death threats?
>
> I think you need to explain more what you are hoping to accomplish.
> In general there are two ways to store multidimensional data:
>
> 1) jagged - with arrays of arrays.  This is the method directly
> supported by D arrays.
>     With this accessing each element requires as many indirections as
> there are dimensions.
>     But for large arrays, this is more friendly to memory use because
> the data doesn't have to be in one huge contiguous chunk
>
> 2) rectangular - with indexing into a chunk of memory.  This method is
> directly supported by some languages like C#, but not D.
>     Accessing each element requires just one indirection but a bit of
> offset computation.
>     Very large arrays may have trouble fitting in available memory.
>    (See this very old proposal for adding them to D:
> http://homepages.uni-regensburg.de/~nen10015/documents/D-multidimarray.html)
>
> Generally if your plan is to do math on these arrays, method 2 is
> better supported by existing math libraries.
> So what do you plan to do with these?  You may be better off
> implementing a rectangular style multi-dim array type than trying to
> use D's built-in.  Or look at the multi-dim array types written by
> Fawzi or myself.
>
> --bb


I started out with no particular plan to this, but have arrived at wanting
to make a range that facilitates "deep foreach" - that is, enumerate all
ranges recursively. This way, it doesn't matter whether one wants to use a
jagged or rectangular array. (except of course possibly for speed)

btw, is there currently a way to support foreach( index, element; range ){}
syntax for ranges? I can't seem to find any documentation on how to get the
index.

-- 
Simen