(octave.info)Access via Handle

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8.2.3 Access via Handle
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A function may be abstracted and referenced via a function handle
acquired using the special operator ‘@’.  For example,

     f = @plus;
     f (2, 2)
     ⇒  4

is equivalent to calling ‘plus (2, 2)’ 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:

     function mydeletefcn (h, ~, msg)
       printf (msg);
     endfunction
     sombrero;
     set (gcf, "deletefcn", {@mydeletefcn, "Bye!\n"});
     close;

The above will print "Bye!"  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, ‘buttondownfcn’,
‘windowscrollwheelfcn’, ‘createfcn’, ‘deletefcn’, ‘keypressfcn’, etc.

   Note that the ‘@’ 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 ‘@’ character.  See Note: Object Oriented
Programming.