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<a name="Precedence-of-Objects"></a>
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<p>
Previous: <a href="Operator-Overloading.html#Operator-Overloading" accesskey="p" rel="prev">Operator Overloading</a>, Up: <a href="Overloading-Objects.html#Overloading-Objects" 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#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Precedence-of-Objects-1"></a>
<h4 class="subsection">34.4.3 Precedence of Objects</h4>
<p>Many functions and operators take two or more arguments and so the
case can easily arise that these functions are called with objects of
different classes. It is therefore necessary to determine the precedence
of which method of which class to call when there are mixed objects given
to a function or operator. To do this the <code>superiorto</code> and
<code>inferiorto</code> functions can be used
</p>
<a name="XREFsuperiorto"></a><dl>
<dt><a name="index-superiorto"></a>Built-in Function: <em></em> <strong>superiorto</strong> <em>(<var>class_name</var>, …)</em></dt>
<dd><p>When called from a class constructor, mark the object currently
constructed as having a higher precedence than <var>class_name</var>.
More that one such class can be specified in a single call.
This function may only be called from a class constructor.
</p>
<p><strong>See also:</strong> <a href="#XREFinferiorto">inferiorto</a>.
</p></dd></dl>
<a name="XREFinferiorto"></a><dl>
<dt><a name="index-inferiorto"></a>Built-in Function: <em></em> <strong>inferiorto</strong> <em>(<var>class_name</var>, …)</em></dt>
<dd><p>When called from a class constructor, mark the object currently
constructed as having a lower precedence than <var>class_name</var>.
More that one such class can be specified in a single call.
This function may only be called from a class constructor.
</p>
<p><strong>See also:</strong> <a href="#XREFsuperiorto">superiorto</a>.
</p></dd></dl>
<p>For example with our polynomial class consider the case
</p>
<div class="example">
<pre class="example">2 * polynomial ([1, 0, 1]);
</pre></div>
<p>That mixes an object of the class <code>"double"</code> with an object of the class
<code>"polynomial"</code>. In this case we like to ensure that the return type of
the above is of the type <code>"polynomial"</code> and so we use the
<code>superiorto</code> function in the class constructor. In particular our
polynomial class constructor would be modified to be
</p>
<div class="example">
<pre class="verbatim">## -*- texinfo -*-
## @deftypefn {Function File} {} polynomial ()
## @deftypefnx {Function File} {} polynomial (@var{a})
## Create a polynomial object representing the polynomial
##
## @example
## a0 + a1 * x + a2 * x^2 + @dots{} + an * x^n
## @end example
##
## @noindent
## from a vector of coefficients [a0 a1 a2 @dots{} an].
## @end deftypefn
function p = polynomial (a)
if (nargin == 0)
p.poly = [0];
p = class (p, "polynomial");
elseif (nargin == 1)
if (strcmp (class (a), "polynomial"))
p = a;
elseif (isvector (a) && isreal (a))
p.poly = a(:).';
p = class (p, "polynomial");
else
error ("polynomial: expecting real vector");
endif
else
print_usage ();
endif
superiorto ("double");
endfunction
</pre><pre class="example">
</pre></div>
<p>Note that user classes always have higher precedence than built-in
Octave types. So in fact marking our polynomial class higher than the
<code>"double"</code> class is in fact not necessary.
</p>
<p>When faced with two objects that have the same precedence, Octave will use the
method of the object that appears first on the list of arguments.
</p>
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Previous: <a href="Operator-Overloading.html#Operator-Overloading" accesskey="p" rel="prev">Operator Overloading</a>, Up: <a href="Overloading-Objects.html#Overloading-Objects" 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#Concept-Index" title="Index" rel="index">Index</a>]</p>
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