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Re: data type polymorphism

From: Riccardo Mottola
Subject: Re: data type polymorphism
Date: Sat, 21 Mar 2015 10:19:21 +0100
User-agent: Mozilla/5.0 (X11; FreeBSD i386; rv:35.0) Gecko/20100101 Firefox/35.0 SeaMonkey/2.32

Hi Scott,

Scott Christley wrote:

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.


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.


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