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.