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Previous: <a href="Recursion.html" accesskey="p" rel="prev">Recursion</a>, Up: <a href="Calling-Functions.html" accesskey="u" rel="up">Calling Functions</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="Access-via-Handle-1"><span>8.2.3 Access via Handle<a class="copiable-link" href="#Access-via-Handle-1"> ¶</a></span></h4>
<a class="index-entry-id" id="index-function-handle"></a>
<a class="index-entry-id" id="index-indirect-function-call"></a>
<a class="index-entry-id" id="index-_0040-function-handle"></a>
<p>A function may be abstracted and referenced via a function handle acquired
using the special operator ‘<samp class="samp">@</samp>’. For example,
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">f = @plus;
f (2, 2)
⇒ 4
</pre></div></div>
<p>is equivalent to calling <code class="code">plus (2, 2)</code> directly. Beyond abstraction for
general programming, function handles find use in callback methods for figures
and graphics by adding listeners to properties or assigning pre-existing
actions, such as in the following example:
</p>
<a class="index-entry-id" id="index-figure-deletefcn"></a>
<div class="example">
<div class="group"><pre class="example-preformatted">function mydeletefcn (h, ~, msg)
printf (msg);
endfunction
sombrero;
set (gcf, "deletefcn", {@mydeletefcn, "Bye!\n"});
close;
</pre></div></div>
<p>The above will print <code class="code">"Bye!"</code> to the terminal upon the closing
(deleting) of the figure. There are many graphics property actions for which
a callback function may be assigned, including, <code class="code">buttondownfcn</code>,
<code class="code">windowscrollwheelfcn</code>, <code class="code">createfcn</code>, <code class="code">deletefcn</code>,
<code class="code">keypressfcn</code>, etc.
</p>
<p>Note that the ‘<samp class="samp">@</samp>’ character also plays a role in defining class
functions, i.e., methods, but not as a syntactical element. Rather it begins a
directory name containing methods for a class that shares the directory name
sans the ‘<samp class="samp">@</samp>’ character. See <a class="ref" href="Object-Oriented-Programming.html">Object Oriented Programming</a>.
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