UNIVERSAL::can

UNIVERSAL::can(3pm)   User Contributed Perl Documentation  UNIVERSAL::can(3pm)



NAME
       UNIVERSAL::can - Hack around people calling UNIVERSAL::can() as a func-
       tion

VERSION
       Version 1.01

SYNOPSIS
       To use this module, simply:

         use UNIVERSAL::can;

DESCRIPTION
       The UNIVERSAL class provides a few default methods so that all objects
       can use them.  Object orientation allows programmers to override these
       methods in subclasses to provide more specific and appropriate behav-
       ior.

       Some authors call methods in the UNIVERSAL class on potential invocants
       as functions, bypassing any possible overriding.  This is wrong and you
       should not do it.  Unfortunately, not everyone heeds this warning and
       their bad code can break your good code.

       This module replaces "UNIVERSAL::can()" with a method that checks to
       see if the first argument is a valid invocant (whether an object -- a
       blessed referent -- or the name of a class).  If so, and if the invo-
       cant's class has its own "can()" method, it calls that as a method.
       Otherwise, everything works as you might expect.

       If someone attempts to call "UNIVERSAL::can()" as a function, this mod-
       ule will emit a lexical warning (see perllexwarn) to that effect.  You
       can disable it with "no warnings;" or "no warnings 'UNIVERSAL::isa';",
       but don't do that; fix the code instead.

       Some people argue that you must call "UNIVERSAL::can()" as a function
       because you don't know if your proposed invocant is a valid invocant.
       That's silly.  Use "blessed()" from Scalar::Util if you want to check
       that the potential invocant is an object or call the method anyway in
       an "eval" block and check for failure.

       Just don't break working code.

EXPORT
       This module can optionally export a "can()" subroutine that works
       exactly as described.  It's a convenient shortcut for you.  This actu-
       ally works in version 1.11.

       Also, if you pass the "-always_warn" flag on the import line, this mod-
       ule will warn about all incorrect uses of "UNIVERSAL::can()".  This can
       help you change your code to be correct.

       can()

       The "can()" method takes two arguments, a potential invocant and the
       name of a method that that invocant may be able to call.  It attempts
       to divine whether the invocant is an object or a valid class name,
       whether there is an overridden "can()" method for it, and then calls
       that.  Otherwise, it calls "UNIVERSAL::can()" directly, as if nothing
       had happened.

AUTHOR
       chromatic, "<chromatic AT wgz.org>"

BUGS
       Please report any bugs or feature requests to "bug-univer-
       sal-can AT rt.org", or through the web interface at
       <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=UNIVERSAL-can>;.  This
       will contact me, hold onto patches so I don't drop them, and will
       notify you of progress on your request as I make changes.

ACKNOWLEDGEMENTS
       Inspired by UNIVERSAL::isa by Yuval Kogman, Autrijus Tang, and myself.

       Adam Kennedy has tirelessly made me tired by reporting potential bugs
       and suggesting ideas that found actual bugs.

       Mark Clements helped to track down an invalid invocant bug.

COPYRIGHT & LICENSE
       Copyright (c) 2005 - 2006 chromatic. All rights reserved.

       This program is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.



perl v5.8.8                       2006-04-01               UNIVERSAL::can(3pm)