Monday, February 1, 2010


I've been meaning to write about this gotcha for a long time, but somehow forgot. This was actually an undiscovered bug in Moose for several years:

use strict;
use warnings;

use Test::More;

use Try::Tiny qw(try);

    package Foo;

    use Scalar::Util qw(blessed);

    sub new { bless {}, $_[0] }

my $foo = Foo->new;

is( try { blessed($foo) }, undef );

is( try { blessed $foo }, undef );


The first test passes. blessed has't been imported into main, so the code results in the error Undefined subroutine &main::blessed.

The second test, on the other hand, fails. This is because blessed has been invoked as a method on $foo.

The Moose codebase had several instances of if ( blessed $object ), in packages that did not import blessed at all. This worked for ages, because Moose::Object, the base class for most objects in the Moose ecosystem, didn't clean up that export, and therefore provided an inherited blessed method for pretty much any class written in Moose.

I think this example provides a very strong case for using namespace::clean or namespace::autoclean routinely in your classes.

To cover the other half of the problem, the no indirect pragma allows the removal of this unfortunate feature from specific lexical scopes.