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Next: <a href="Operator-Overloading.html" accesskey="n" rel="next">Operator Overloading</a>, Up: <a href="Overloading-Objects.html" accesskey="u" rel="up">Overloading Objects</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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<h4 class="subsection" id="Function-Overloading-1"><span>34.4.1 Function Overloading<a class="copiable-link" href="#Function-Overloading-1"> ¶</a></span></h4>
<p>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 <code class="code">polyval</code> function.
</p>
<div class="example">
<div class="group"><pre class="verbatim">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
</pre></div></div>
<p>This function just hands off the work to the normal Octave <code class="code">polyval</code>
function. Another interesting example of an overloaded function for the
polynomial class is the <code class="code">plot</code> function.
</p>
<div class="example">
<div class="group"><pre class="verbatim">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
</pre></div></div>
<p>which allows polynomials to be plotted in the domain near the region of the
roots of the polynomial.
</p>
<p>Functions that are of particular interest for overloading are the class
conversion functions such as <code class="code">double</code>. Overloading these functions allows
the <code class="code">cast</code> 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 <code class="code">double</code> function for the polynomial class might look like
</p>
<div class="example">
<div class="group"><pre class="verbatim">function a = double (p)
a = p.poly;
endfunction
</pre></div></div>
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