package MooseX::UndefTolerant::Attribute;

our $VERSION = '0.21';

use Moose::Role;
use namespace::autoclean;

around('initialize_instance_slot', sub {
    my $orig = shift;
    my $self = shift;
    my ($meta_instance, $instance, $params) = @_;

    my $key_name = $self->init_arg;

    # If our parameter passed in was undef, remove it from the parameter list...
    # but leave the value unscathed if the attribute's type constraint can
    # handle undef (or doesn't have one, which implicitly means it can)
    if (defined $key_name and not defined($params->{$key_name}))
    {
        my $type_constraint = $self->type_constraint;
        if ($type_constraint and not $type_constraint->check(undef))
        {
            delete $params->{$key_name};
        }
    }

    # Invoke the real init, as the above line cleared the undef param value
    $self->$orig(@_)
});

1;

# ABSTRACT: Make your attribute(s) tolerant to undef initialization

__END__

=pod

=encoding UTF-8

=head1 NAME

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

=head1 VERSION

version 0.21

=head1 SYNOPSIS

  package My:Class;
  use Moose;

  use MooseX::UndefTolerant::Attribute;

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

  # Meanwhile, under the city...

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

=head1 DESCRIPTION

Applying this trait to your attribute makes its initialization tolerant of
of undef.  If you specify the value of undef to any of the attributes they
will not be initialized (or will be set to the default, if applicable).
Effectively behaving as if you had not provided a value at all.

=head1 SUPPORT

Bugs may be submitted through L<the RT bug tracker|https://rt.cpan.org/Public/Dist/Display.html?Name=MooseX-UndefTolerant>
(or L<bug-MooseX-UndefTolerant@rt.cpan.org|mailto:bug-MooseX-UndefTolerant@rt.cpan.org>).

There is also a mailing list available for users of this distribution, at
L<http://lists.perl.org/list/moose.html>.

There is also an irc channel available for users of this distribution, at
L<C<#moose> on C<irc.perl.org>|irc://irc.perl.org/#moose>.

=head1 AUTHOR

Cory G Watson <gphat at cpan.org>

=head1 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.

=cut