---
name: "Perl::Critic::Policy::BuiltinFunctions::ProhibitUniversalIsa"
section: "3pm"
platform: "linux"
package: "perl-perl-critic"
version: "1.156-3"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/Perl::Critic::Policy::BuiltinFunctions::ProhibitUniversalIsa"
---

# Perl::Critic::Policy::BuiltinFunctions::ProhibitUniversalIsa(3pm)

Write "eval { $foo-\>isa($pkg) }" instead of "UNIVERSAL::isa($foo, $pkg)".

## NAME

Perl::Critic::Policy::BuiltinFunctions::ProhibitUniversalIsa - Write "eval { $foo-\>isa($pkg) }" instead of "UNIVERSAL::isa($foo, $pkg)".

## AFFILIATION

This Policy is part of the core Perl::Critic distribution.

## DESCRIPTION

```
    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 UNIVERSAL::isa for an incendiary discussion of this topic.

## CONFIGURATION

This Policy is not configurable except for the standard options.

## SEE ALSO

Perl::Critic::Policy::BuiltinFunctions::ProhibitUniversalCan

## AUTHOR

Chris Dolan \<cdolan@cpan.org\>

## COPYRIGHT

Copyright (c) 2006-2023 Chris Dolan.

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.