(octave.info)Function Overloading

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34.4.1 Function Overloading
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Any Octave function can be overloaded, and this allows an
object-specific version of a function to be called as needed.  A
pertinent example for the polynomial class might be to overload the
‘polyval’ function.

     function [y, dy] = polyval (p, varargin)
     
       if (nargout > 1)
         [y, dy] = polyval (fliplr (p.poly), varargin{:});
       else
         y = polyval (fliplr (p.poly), varargin{:});
       endif
     
     endfunction

   This function just hands off the work to the normal Octave ‘polyval’
function.  Another interesting example of an overloaded function for the
polynomial class is the ‘plot’ function.

     function h = plot (p, varargin)
     
       n = 128;
       rmax = max (abs (roots (p.poly)));
       x = [0 : (n - 1)] / (n - 1) * 2.2 * rmax - 1.1 * rmax;
       if (nargout > 0)
         h = plot (x, polyval (p, x), varargin{:});
       else
         plot (x, polyval (p, x), varargin{:});
       endif
     
     endfunction

which allows polynomials to be plotted in the domain near the region of
the roots of the polynomial.

   Functions that are of particular interest for overloading are the
class conversion functions such as ‘double’.  Overloading these
functions allows the ‘cast’ function to work with a user class.  It can
also aid in the use of a class object with methods and functions from
other classes since the object can be transformed to the requisite input
form for the new function.  An example ‘double’ function for the
polynomial class might look like

     function a = double (p)
       a = p.poly;
     endfunction