print UNIVERSAL::isa($obj, 'Foo::Bar') ? 'yes' : 'no';  #not ok
  print eval { $obj->isa('Foo::Bar') } ? 'yes' : 'no';    #ok

As of Perl 5.9.3, the use of UNIVERSAL::isa as a function has been deprecated and the method form is preferred instead. Formerly, the functional form was recommended because it gave valid results even when the object was undef or an unblessed scalar. However, the functional form makes it impossible for packages to override isa(), a technique which is crucial for implementing mock objects and some facades.

Another alternative to UNIVERSAL::isa is the _INSTANCE method of Param::Util, which is faster.

See the CPAN module the UNIVERSAL::isa manpage for an incendiary discussion of this topic.


the Perl::Critic::Policy::BuiltinFunctions::ProhibitUniversalCan manpage


Chris Dolan <cdolan@cpan.org>


Copyright (c) 2006 Chris Dolan. All rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. The full text of this license can be found in the LICENSE file included with this module.