moosex::undeftolerant(3pm) [debian man page]

MooseX::UndefTolerant(3pm)				User Contributed Perl Documentation				MooseX::UndefTolerant(3pm)

NAME

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

VERSION

       version 0.17

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 quandry:

	 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>

COPYRIGHT AND LICENSE

       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.

perl v5.14.2							    2012-05-03						MooseX::UndefTolerant(3pm)

Check Out this Related Man Page

Moose::Cookbook::Meta::WhyMeta(3)			User Contributed Perl Documentation			 Moose::Cookbook::Meta::WhyMeta(3)

NAME

       Moose::Cookbook::Meta::WhyMeta - Welcome to the meta world (Why Go Meta?)

VERSION

       version 2.0604

SUMMARY

       You might want to read Moose::Manual::MOP if you haven't done so yet.

       If you've ever thought "Moose is great, but I wish it did X differently", then you've gone meta. The meta recipes demonstrate how to change
       and extend the way Moose works by extending and overriding how the meta classes (Moose::Meta::Class, Moose::Meta::Attribute, etc) work.

       The metaclass API is a set of classes that describe classes, roles, attributes, etc. The metaclass API lets you ask questions about a
       class, like "what attributes does it have?", or "what roles does the class do?"

       The metaclass system also lets you make changes to a class, for example by adding new methods or attributes.

       The interface presented by Moose.pm ("has", "with", "extends") is just a thin layer of syntactic sugar over the underlying metaclass
       system.

       By extending and changing how this metaclass system works, you can create your own Moose variant.

   Examples
       Let's say that you want to add additional properties to attributes. Specifically, we want to add a "label" property to each attribute, so
       we can write "My::Class->meta()->get_attribute('size')->label()". The first recipe shows how to do this using an attribute trait.

       You might also want to add additional properties to your metaclass. For example, if you were writing an ORM based on Moose, you could
       associate a table name with each class via the class's metaclass object, letting you write "My::Class->meta()->table_name()".

SEE ALSO

       Many of the MooseX modules on CPAN implement metaclass extensions. A couple good examples include MooseX::Aliases and
       MooseX::UndefTolerant. For a more complex example see Fey::ORM or Bread::Board::Declare.

AUTHOR

       Moose is maintained by the Moose Cabal, along with the help of many contributors. See "CABAL" in Moose and "CONTRIBUTORS" in Moose for
       details.

COPYRIGHT AND LICENSE

       This software is copyright (c) 2012 by Infinity Interactive, Inc..

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

perl v5.16.2							    2012-09-19					 Moose::Cookbook::Meta::WhyMeta(3)

Linux and UNIX Man Pages

moosex::undeftolerant(3pm) [debian man page]

Check Out this Related Man Page