<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ --> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>Access via Handle (GNU Octave (version 5.1.0))</title> <meta name="description" content="Access via Handle (GNU Octave (version 5.1.0))"> <meta name="keywords" content="Access via Handle (GNU Octave (version 5.1.0))"> <meta name="resource-type" content="document"> <meta name="distribution" content="global"> <meta name="Generator" content="makeinfo"> <link href="index.html#Top" rel="start" title="Top"> <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> <link href="Calling-Functions.html#Calling-Functions" rel="up" title="Calling Functions"> <link href="Arithmetic-Ops.html#Arithmetic-Ops" rel="next" title="Arithmetic Ops"> <link href="Recursion.html#Recursion" rel="prev" title="Recursion"> <style type="text/css"> <!-- a.summary-letter {text-decoration: none} blockquote.indentedblock {margin-right: 0em} blockquote.smallindentedblock {margin-right: 0em; font-size: smaller} blockquote.smallquotation {font-size: smaller} div.display {margin-left: 3.2em} div.example {margin-left: 3.2em} div.lisp {margin-left: 3.2em} div.smalldisplay {margin-left: 3.2em} div.smallexample {margin-left: 3.2em} div.smalllisp {margin-left: 3.2em} kbd {font-style: oblique} pre.display {font-family: inherit} pre.format {font-family: inherit} pre.menu-comment {font-family: serif} pre.menu-preformatted {font-family: serif} pre.smalldisplay {font-family: inherit; font-size: smaller} pre.smallexample {font-size: smaller} pre.smallformat {font-family: inherit; font-size: smaller} pre.smalllisp {font-size: smaller} span.nolinebreak {white-space: nowrap} span.roman {font-family: initial; font-weight: normal} span.sansserif {font-family: sans-serif; font-weight: normal} ul.no-bullet {list-style: none} --> </style> <link rel="stylesheet" type="text/css" href="octave.css"> </head> <body lang="en"> <a name="Access-via-Handle"></a> <div class="header"> <p> Previous: <a href="Recursion.html#Recursion" accesskey="p" rel="prev">Recursion</a>, Up: <a href="Calling-Functions.html#Calling-Functions" 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#Concept-Index" title="Index" rel="index">Index</a>]</p> </div> <hr> <a name="Access-via-Handle-1"></a> <h4 class="subsection">8.2.3 Access via Handle</h4> <a name="index-function-handle"></a> <a name="index-indirect-function-call"></a> <a name="index-_0040-function-handle"></a> <p>A function may be abstracted and referenced via a function handle acquired using the special operator ‘<samp>@</samp>’. For example, </p> <div class="example"> <pre class="example">f = @plus; f (2, 2) ⇒ 4 </pre></div> <p>is equivalent to calling <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 name="index-figure-deletefcn"></a> <div class="example"> <pre class="example">function mydeletefcn (h, ~, msg) printf (msg); endfunction sombrero; set (gcf, "deletefcn", {@mydeletefcn, "Bye!\n"}); close; </pre></div> <p>The above will print <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>buttondownfcn</code>, <code>windowscrollwheelfcn</code>, <code>createfcn</code>, <code>deletefcn</code>, <code>keypressfcn</code>, etc. </p> <p>Note that the ‘<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>@</samp>’ character. See <a href="Object-Oriented-Programming.html#Object-Oriented-Programming">Object Oriented Programming</a>. </p> </body> </html>