NAME

       MooseX::UndefTolerant - Make your attribute(s) tolerant to undef initialization

VERSION

       version 0.20

SYNOPSIS

         package My::Class;

         use Moose;
         use MooseX::UndefTolerant;

         has 'name' => (
           is => 'ro',
           isa => 'Str',
           predicate => 'has_name'
         );

         # Meanwhile, under the city...

         # Doesn't explode
         my $class = My::Class->new(name => undef);
         $class->has_name # False!

       Or, if you only want one attribute to have this behaviour:

         package My:Class;
         use Moose;

         use MooseX::UndefTolerant::Attribute;

         has 'bar' => (
             traits => [ qw(MooseX::UndefTolerant::Attribute)],
             is => 'ro',
             isa => 'Num',
             predicate => 'has_bar'
         );

DESCRIPTION

       Loading this module in your Moose class makes initialization of your attributes tolerant
       of undef.  If you specify the value of undef to any of the attributes they will not be
       initialized, effectively behaving as if you had not provided a value at all.

       You can also apply the 'UndefTolerant' trait to individual attributes. See
       MooseX::UndefTolerant::Attribute for details.

       There will be no change in behaviour to any attribute with a type constraint that accepts
       undef values (for example "Maybe" types), as it is presumed that since the type is already
       "undef tolerant", there is no need to avoid initializing the attribute value with "undef".

       As of Moose 1.9900, this module can also be used in a role, in which case all of that
       role's attributes will be undef-tolerant.

MOTIVATION

       I often found myself in this quandary:

         package My:Class;
         use Moose;

         has 'foo' => (
           is => 'ro',
           isa => 'Str',
         );

         # ... then

         my $foo = ... # get the param from something

         my $class = My:Class->new(foo => $foo, bar => 123);

       What if foo is undefined?  I didn't want to change my attribute to be Maybe[Str] and I
       still want my predicate ("has_foo") to work.  The only real solution was:

         if(defined($foo)) {
           $class = My:Class->new(foo => $foo, bar => 123);
         } else {
           $class = My:Class->new(bar => 123);
         }

       Or some type of codemulch using ternary conditionals.  This module allows you to make your
       attributes more tolerant of undef so that you can keep the first example: have your cake
       and eat it too!

PER ATTRIBUTE

       See MooseX::UndefTolerant::Attribute.

CAVEATS

       This extension does not currently work in immutable classes when applying the trait to
       some (but not all) attributes in the class. This is because the inlined constructor
       initialization code currently lives in Moose::Meta::Class, not Moose::Meta::Attribute. The
       good news is that this is expected to be changing shortly.

ACKNOWLEDGEMENTS

       Many thanks to the crew in #moose who talked me through this module:

           Hans Dieter Pearcey (confound) Jesse Luehrs (doy) Tomas Doran (t0m) Dylan Hardison
           (dylan) Jay Shirley (jshirley) Mike Eldridge (diz)

AUTHOR

       Cory G Watson <gphat at cpan.org>

CONTRIBUTORS

       •   Karen Etheridge <ether@cpan.org>

       •   Dave Rolsky <autarch@urth.org>

       •   Cory G Watson <gphat@cpan.org>

       •   Jesse Luehrs <doy@tozt.net>

       •   Chris Andrews <chrisandrews@venda.com>

COPYRIGHT AND LICENCE

       This software is copyright (c) 2011 by Cory G Watson.

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