UNIVERSAL::isa(3) Attempt to recover from people calling UNIVERSAL::isa as a function


version 1.20150614


# 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';


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.


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.




This software is copyright (c) 2011 by [email protected].

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.