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data type polymorphism

From: Scott Christley
Subject: data type polymorphism
Date: Fri, 20 Mar 2015 14:39:23 -0500


This is more a generic Objective-C question versus GNUstep but maybe some experts here have a suggestion.

I have a bunch of code that looks l like this:

  if ([encode isEqual: [BioSwarmModel floatEncode]]) {
    // 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;

  } else if ([encode isEqual: [BioSwarmModel doubleEncode]]) {
    // 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:

    for (i = 0;i < height; ++i)
      for (j = 0;j < width; ++j)
          (*grid)[i][j] = 0.0;

So is there some new Objective-C feature that I’m unaware of which can do this for me?

I know at the C language level, there essentially has to be separate code generated for each data type.  I can do some trickery with C-preprocessor macros, or #include code snippets but I’ve avoided that at the moment.


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