Re: [Boost-users] question about multi_array use

On Sat, Aug 8, 2009 at 4:51 PM, Alle Meije Wink wrote:

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You could always just wrap up each of the possible dimensions in a struct that can handle the (de)serialization and everything too, perhaps use crtp to put identical functionality in a non-virtual base class.

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Overmind, I guess compared to what I had in mind (define the data container of the image [template?] class as a multi_array with a dimensionality given as a size_t parameter), the CRTP struct you are talking about specifies all of the possible types. Is that correct?

If I understand it correctly then this does what I want, but does that mean that in the worst-case scenario, I have to write out the functionality for all different dimensionalities? If the parameterised template class idea is possible, that would save some typing!

I could see using fusion (mostly the "apply" construct) would make it generic to any number of dimensions. Boost.Fusion is amazing for such work, think MPL, but it works at runtime too.

I like the look of boost::Fusion in terms of advanced generic C++ programming, but in terms of finding a concise description of my image template class / class / data type, this may be overshooting the aim a bit. Plus I will need to read up on template metaprogramming! Coming back to the original idea: my images are stored as files which have a (on-disc 1-dimensional) sequence of intensities, and a header containing a number dims (dimensionality) and an array dim[8] (maximum of 8 dimensions). The problem that images can have different (but all built-in) data types can be circumvented with template programming, which is great compared to the old C-style casting to double. But talking about C-style, dealing with dimensions was possible in a fast way (in terms of both coding and runnning) with malloc and pointers (to pointers (to pointers)). Previously this is how I used to implement operations on images: casting everything to double, using pointers to get to image elements. I was hoping that by using templates to abstract from element type, and multi_array to cover different dimensionalities, it would be possible code image operations only once, for all types and dimensionalities. From what I understand, the curious recursion way matches most closely what I was looking for (and is still as close to generic programming as possible?). The scopira narray class http://www.scopira.org/api/narray_8h-source.html seems to do something similar. If there is another way to do this then I'm still very interested! Thanks, Alle Meije