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UNIVERSAL::can(3) User Contributed Perl Documentation UNIVERSAL::can(3)
UNIVERSAL::can - work around buggy code calling UNIVERSAL::can() as a function
To use this module, simply:
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
This module replaces "UNIVERSAL::can()" with a method that checks to see if the first
argument is a valid invocant has its own "can()" method. If so, it gives a warning and
calls the overridden method, working around buggy code. Otherwise, everything works as
you might expect.
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 (though check the exception
returned, as a poorly-written "can()" method could break Liskov and throw an exception
other than "You can't call a method on this type of invocant").
Just don't break working code.
Please report any bugs or feature requests to "firstname.lastname@example.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.
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.
Curtis "Ovid" Poe finally provided the inspiration I needed to clean up the interface.
Peter du Marchie van Voorthuysen identified and fixed a problem with calling "SUPER::can".
Daniel LeWarne found and fixed a deep recursion error.
Norbert Buchmueller fixed an overloading bug in blessed invocants.
The Perl QA list had a huge... discussion... which inspired my realization that this
module needed to do what it does now.
COPYRIGHT & LICENSE
Copyright (c) 2005 - 2011, chromatic. This module is made available under the same terms
as Perl 5.12.
Hey! The above document had some coding errors, which are explained below:
Around line 146:
Non-ASCII character seen before =encoding in 'Buchmueller'. Assuming UTF-8
perl v5.16.3 2012-07-26 UNIVERSAL::can(3)
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