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UNIVERSAL::can
Hack around people calling UNIVERSAL::can as a function

UNIVERSAL::can - Hack around people calling UNIVERSAL::can as a function


NAME

UNIVERSAL::can - Hack around people calling UNIVERSAL::can() as a function


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 behavior.

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 invocant'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 module 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 the Scalar::Util manpage 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 actually works in version 1.11.

Also, if you pass the -always_warn flag on the import line, this module 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@wgz.org>


BUGS

Please report any bugs or feature requests to bug-universal-can@rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html. 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 the UNIVERSAL::isa manpage 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.

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