#### 34.4.1 Function Overloading ¶

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