Access via Handle (GNU Octave (version 11.0.90))

#### 8.2.3 Access via Handle ¶

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 Object Oriented Programming.