NAME
    Callback - object interface for function callbacks

SYNOPSIS
            use Callback;

            my $callback = new Callback (\&myfunc, @myargs);
            my $callback = new Callback ($myobj, $mymethod, @myargs);
            my $callback = new Callback ($old_callback, @myargs);

            $callback->call(@some_more_args);

DESCRIPTION
    Callback provides a standard interface to register callbacks. Those
    callbacks can be either purely functional (i.e. a function call with
    arguments) or object-oriented (a method call on an object).

    When a callback is constructed, a base set of arguments can be provided.
    These function arguments will preceed any arguments added at the time
    the call is made.

    There are two forms for the callback constructor, depending on whether
    the call is a pure functional call or a method call. The rule is that if
    the first argument is an object, then the second argument is a method
    name to be called on that object. Method resolution happens at the time
    the Callback object is built: an error will be raised if it cannot be
    found.

    Callback objects built for object-oriented calls also have the property
    of being serializable via Storable. Purely functional callabacks cannot
    be serialized because CODE references are not supported by Storable.

    Callback objects can be created from existing Callback objects. Any
    arguments will be appended onto the original list of arguments.

TRACING
            use Callback qw(@callbackTrace);

    If you're writing a debugging routine that provides a stack-dump (for
    example, Carp::confess) it is useful to know where a callback was
    registered.

            my $ct = 0;
            while (($package, $file, $line, $subname, $hasargs, $wantarray) = caller($i++)) {
                ...

                if ($subname eq 'Callback::call') {
                    print "callback registered $Callback::callbackTrace[$ct]\n";
                    $ct++;
                }
            }

    Without such code, it becomes very hard to know what's going on.

COPYRIGHT
    Copyright (C) 1994, 2000, 2002 David Muir Sharnoff. All rights reserved.
    License hearby granted for anyone to use this module at their own risk.
    Please feed useful changes back to muir@idiom.com.

AUTHORS
    David Muir Sharnoff <muir@idiom.com> and Raphael Manfredi
    <Raphael_Manfredi@pobox.com>

SEE ALSO
    Storable(3).