Re: data type polymorphism

[Riccardo Mottola]

Hi Scott,


Scott Christley wrote:
> Hello,
>
> This is more a generic Objective-C question versus GNUstep but maybe 
> some experts here have a suggestion.

I think this is a more a "C" question since it involves pointer sizes 
and such.

> I have a bunch of code that looks l like this:
>
>
> if([encodeisEqual: [BioSwarmModelfloatEncode]]) {
>     // interpret as float matrix
> float (*grid)[height][width] = matrix;
> for (i = 0;i < height; ++i)
> for (j = 0;j < width; ++j)
>           (*grid)[i][j] = 0.0;
>
>   } elseif([encodeisEqual: [BioSwarmModeldoubleEncode]]) {
>   // interpret as double matrix
> double (*grid)[height][width] = matrix;
> for (i = 0;i < height; ++i)
> for (j = 0;j < width; ++j)
>         (*grid)[i][j] = 0.0;
>    }
>
>
> where I have a generic pointer void *matrix to some data, that I need 
> to interpret as a specific data type, generally either int, float or 
> double.  The part I don’t like is that the operation is essentially 
> identical regardless of the data type, but I have to duplicate code in 
> order to handle it.  In this example, the code is just zero’ing out 
> the data.  This can be a pain for more complicated operations as I 
> have to make sure I do the correct changes to each code piece.  What I 
> would like is just to write the code once and have the compiler or 
> whatever handle the data type for me:

I have a very similar problem I suppose. To reply to max: no, I can't 
just use double, the pointer size changes. I want to read out both 8 and 
16 bit images.

http://price.cvs.sourceforge.net/viewvc/price/PRICE-osx/PRInvert.m?revision=1.13&view=markup

Here I have the same code twice, actually even the same loop, what 
changes is that I declared the image data pointers once as unsigned 
char, once as unsigned short. I want to support this at runtime, so no 
#ifdef compile-time trickery.

This stopped me from making all filters support 16 bit images because it 
would mean rewriting half of the application this way.

Riccardo