NAME

       UNIVERSAL::isa - recover from people calling UNIVERSAL::isa as a function

SYNOPSIS

           # from the shell
           echo 'export PERL5OPT=-MUNIVERSAL::isa' >> /etc/profile

           # within your program
           use UNIVERSAL::isa;

           # enable warnings for all dodgy uses of UNIVERSAL::isa
           use UNIVERSAL::isa 'verbose';

DESCRIPTION

       Whenever you use "isa" in UNIVERSAL as a function, a kitten using Test::MockObject dies.
       Normally, the kittens would be helpless, but if they use UNIVERSAL::isa (the module whose
       docs you are reading), the kittens can live long and prosper.

       This module replaces "UNIVERSAL::isa" with a version that makes sure that, when called as
       a function on objects which override "isa", "isa" will call the appropriate method on
       those objects

       In all other cases, the real "UNIVERSAL::isa" gets called directly.

       NOTE: You should use this module only for debugging purposes. It does not belong as a
       dependency in running code.

WARNINGS

       If the lexical warnings pragma is available, this module will emit a warning for each
       naughty invocation of "UNIVERSAL::isa". Silence these warnings by saying:

           no warnings 'UNIVERSAL::isa';

       in the lexical scope of the naughty code.

       After version 1.00, warnings only appear when naughty code calls UNIVERSAL::isa() as a
       function on an invocant for which there is an overridden isa().  These are really truly
       active bugs, and you should fix them rather than relying on this module to find them.

       To get warnings for all potentially dangerous uses of UNIVERSAL::isa() as a function, not
       a method (that is, for all uses of the method as a function, which are latent bugs, if not
       bugs that will break your code as it exists now), pass the "verbose" flag when using the
       module.  This can generate many extra warnings, but they're more specific as to the actual
       wrong practice and they usually suggest proper fixes.

SEE ALSO

       Perl::Critic::Policy::BuiltinFunctions::ProhibitUniversalIsa

       UNIVERSAL::can for another discussion of the problem at hand.

       Test::MockObject for one example of a module that really needs to override "isa()".

       Any decent explanation of OO to understand why calling methods as functions is a
       staggeringly bad idea.

AUTHORS

       Audrey Tang <cpan@audreyt.org>

       chromatic <chromatic@wgz.org>

       Yuval Kogman <nothingmuch@woobling.org>

COPYRIGHT & LICENSE

       Copyright (c) 2005 - 2011, chromatic. This module is made available under the same terms
       as Perl 5.12.