Provided by: libmoosex-attributeshortcuts-perl_0.037-2_all 
NAME
MooseX::AttributeShortcuts - Shorthand for common attribute options
VERSION
This document describes version 0.037 of MooseX::AttributeShortcuts - released November
20, 2017 as part of MooseX-AttributeShortcuts.
SYNOPSIS
package Some::Class;
use Moose;
use MooseX::AttributeShortcuts;
# same as:
# is => 'ro', lazy => 1, builder => '_build_foo'
has foo => (is => 'lazy');
# same as: is => 'ro', writer => '_set_foo'
has foo => (is => 'rwp');
# same as: is => 'ro', builder => '_build_bar'
has bar => (is => 'ro', builder => 1);
# same as: is => 'ro', clearer => 'clear_bar'
has bar => (is => 'ro', clearer => 1);
# same as: is => 'ro', predicate => 'has_bar'
has bar => (is => 'ro', predicate => 1);
# works as you'd expect for "private": predicate => '_has_bar'
has _bar => (is => 'ro', predicate => 1);
# extending? Use the "Shortcuts" trait alias
extends 'Some::OtherClass';
has '+bar' => (traits => [Shortcuts], builder => 1, ...);
DESCRIPTION
Ever find yourself repeatedly specifying writers and builders, because there's no good
shortcut to specifying them? Sometimes you want an attribute to have a read-only public
interface, but a private writer. And wouldn't it be easier to just say "builder => 1" and
have the attribute construct the canonical "_build_$name" builder name for you?
This package causes an attribute trait to be applied to all attributes defined to the
using class. This trait extends the attribute option processing to handle the above
variations. All attribute options as described in Moose or Class::MOP::Attribute remain
usable, just as when this trait is not applied.
Some Notes On History
Moose has long had a lazy_build attribute option. It was once considered a best practice,
but that has, ah, changed. This trait began as a desire to still leverage bits of
"lazy_build" (and a tacit acknowledgment that fat-finger bugs rank among the most
embarrassing, right up there with "the TV was unplugged the entire time").
This author does not recommend you use "lazy_build", unless you know exactly what you're
doing (probably) and that it's a good idea (probably not).
Nonetheless, this "lazy_build" option is why we set certain options the way we do below;
while "lazy_build" in its entirety is not optimal, it had the right idea: regular,
predictable accessor names for regular, predictable attribute options.
As an example, just looking at the below it doesn't seem logical that:
has _foo => (is => 'ro', clearer => 1);
...becomes:
has _foo => (is => 'ro', clearer => '_clear_foo');
After reading the lazy_build attribute option, however, we see that the choice had already
been made for us.
USAGE
This package automatically applies an attribute metaclass trait. Simply using this
package causes the trait to be applied by default to your attribute's metaclasses.
EXTENDING A CLASS
If you're extending a class and trying to extend its attributes as well, you'll find out
that the trait is only applied to attributes defined locally in the class. This package
exports a trait shortcut function "Shortcuts" that will help you apply this to the
extended attribute:
has '+something' => (traits => [Shortcuts], ...);
NEW ATTRIBUTE OPTIONS
Unless specified here, all options defined by Moose::Meta::Attribute and
Class::MOP::Attribute remain unchanged.
Want to see additional options? Ask, or better yet, fork on GitHub and send a pull
request. If the shortcuts you're asking for already exist in Moo or Mouse or elsewhere,
please note that as it will carry significant weight.
For the following, $name should be read as the attribute name; and the various prefixes
should be read using the defaults.
is => 'rwp'
Specifying "is => 'rwp'" will cause the following options to be set:
is => 'ro'
writer => "_set_$name"
rwp can be read as "read + write private".
is => 'lazy'
Specifying "is => 'lazy'" will cause the following options to be set:
is => 'ro'
builder => "_build_$name"
lazy => 1
NOTE: Since 0.009 we no longer set "init_arg => undef" if no "init_arg" is explicitly
provided. This is a change made in parallel with Moo, based on a large number of people
surprised that lazy also made one's "init_def" undefined.
is => 'lazy', default => ...
Specifying "is => 'lazy'" and a default will cause the following options to be set:
is => 'ro'
lazy => 1
default => ... # as provided
That is, if you specify "is => 'lazy'" and also provide a "default", then we won't try to
set a builder, as well.
builder => 1
Specifying "builder => 1" will cause the following options to be set:
builder => "_build_$name"
builder => sub { ... }
Passing a coderef to builder will cause that coderef to be installed in the class this
attribute is associated with the name you'd expect, and "builder => 1" to be set.
e.g., in your class (or role),
has foo => (is => 'ro', builder => sub { 'bar!' });
...is effectively the same as...
has foo => (is => 'ro', builder => '_build_foo');
sub _build_foo { 'bar!' }
The behaviour of this option in roles changed in 0.030, and the builder methods will be
installed in the role itself. This means you can alias/exclude/etc builder methods in
roles, just as you can with any other method.
clearer => 1
Specifying "clearer => 1" will cause the following options to be set:
clearer => "clear_$name"
or, if your attribute name begins with an underscore:
clearer => "_clear$name"
(that is, an attribute named "_foo" would get "_clear_foo")
predicate => 1
Specifying "predicate => 1" will cause the following options to be set:
predicate => "has_$name"
or, if your attribute name begins with an underscore:
predicate => "_has$name"
(that is, an attribute named "_foo" would get "_has_foo")
init_arg => 1 / -1
This is a somewhat esoteric shortcut; you probably don't want to use this (or even read
this section).
Specifying "init_arg => 1" will cause the following options to be set:
# attribute: "name"
init_arg => 'name'
# or, attribute: "_name"
init_arg => '_name'
...while "init_arg => -1" will cause the following options to be set:
# attribute: "name"
init_arg => '_name'
# or, attribute: "_name"
init_arg => 'name'
trigger => 1
Specifying "trigger => 1" will cause the attribute to be created with a trigger that calls
a named method in the class with the options passed to the trigger. By default, the
method name the trigger calls is the name of the attribute prefixed with "_trigger_".
e.g., for an attribute named "foo" this would be equivalent to:
trigger => sub { shift->_trigger_foo(@_) }
For an attribute named "_foo":
trigger => sub { shift->_trigger__foo(@_) }
This naming scheme, in which the trigger is always private, is the same as the builder
naming scheme (just with a different prefix).
handles => { foo => sub { ... }, ... }
Creating a delegation with a coderef will now create a new, "custom accessor" for the
attribute. These coderefs will be installed and called as methods on the associated class
(just as readers, writers, and other accessors are), and will have the attribute metaclass
available in $_. Anything the accessor is called with it will have access to in @_, just
as you'd expect of a method.
e.g., the following example creates an attribute named "bar" with a standard reader
accessor named "bar" and two custom accessors named "foo" and "foo_too".
has bar => (
is => 'ro',
isa => 'Int',
handles => {
foo => sub {
my $self = shift @_;
return $_->get_value($self) + 1;
},
foo_too => sub {
my $self = shift @_;
return $self->bar + 1;
},
# ...as you'd expect.
bar => 'bar',
},
);
...and later,
Note that in this example both foo() and foo_too() do effectively the same thing: return
the attribute's current value plus 1. However, foo() accesses the attribute value
directly through the metaclass, the pros and cons of which this author leaves as an
exercise for the reader to determine.
You may choose to use the installed accessors to get at the attribute's value, or use the
direct metaclass access, your choice.
ANONYMOUS SUBTYPING AND COERCION
"Abusus non tollit usum."
Note that we create new, anonymous subtypes whenever the constraint or coercion options
are specified in such a way that the Shortcuts trait (this one) is invoked. It's fully
supported to use both constraint and coerce options at the same time.
This facility is intended to assist with the creation of one-off type constraints and
coercions. It is not possible to deliberately reuse the subtypes we create, and if you
find yourself using a particular isa / constraint / coerce option triplet in more than one
place you should really think about creating a type that you can reuse. MooseX::Types
provides the facilities to easily do this, or even a simple constant definition at the
package level with an anonymous type stashed away for local use.
isa => sub { ... }
has foo => (
is => 'rw',
# $_ == $_[0] == the value to be validated
isa => sub { die unless $_[0] == 1 },
);
# passes constraint
$thing->foo(1);
# fails constraint
$thing->foo(5);
Given a coderef, create a type constraint for the attribute. This constraint will fail if
the coderef dies, and pass otherwise.
Astute users will note that this is the same way Moo constraints work; we use
MooseX::Meta::TypeConstraint::Mooish to implement the constraint.
isa_instance_of => ...
Given a package name, this option will create an "isa" type constraint that requires the
value of the attribute be an instance of the class (or a descendant class) given. That
is,
has foo => (is => 'ro', isa_instance_of => 'SomeThing');
...is effectively the same as:
use Moose::TypeConstraints 'class_type';
has foo => (
is => 'ro',
isa => class_type('SomeThing'),
);
...but a touch less awkward.
isa => ..., constraint => sub { ... }
Specifying the constraint option with a coderef will cause a new subtype constraint to be
created, with the parent type being the type specified in the "isa" option and the
constraint being the coderef supplied here.
For example, only integers greater than 10 will pass this attribute's type constraint:
# value must be an integer greater than 10 to pass the constraint
has thinger => (
isa => 'Int',
constraint => sub { $_ > 10 },
# ...
);
Note that if you supply a constraint, you must also provide an "isa".
isa => ..., constraint => sub { ... }, coerce => 1
Supplying a constraint and asking for coercion will "Just Work", that is, any coercions
that the "isa" type has will still work.
For example, let's say that you're using the "File" type constraint from
MooseX::Types::Path::Class, and you want an additional constraint that the file must
exist:
has thinger => (
is => 'ro',
isa => File,
constraint => sub { !! $_->stat },
coerce => 1,
);
"thinger" will correctly coerce the string "/etc/passwd" to a "Path::Class:File", and will
only accept the coerced result as a value if the file exists.
coerce => [ Type => sub { ...coerce... }, ... ]
Specifying the coerce option with a hashref will cause a new subtype to be created and
used (just as with the constraint option, above), with the specified coercions added to
the list. In the passed hashref, the keys are Moose types (well, strings resolvable to
Moose types), and the values are coderefs that will coerce a given type to our type.
has bar => (
is => 'ro',
isa => 'Str',
coerce => [
Int => sub { "$_" },
Object => sub { 'An instance of ' . ref $_ },
],
);
INTERACTIONS WITH OTHER ATTRIBUTE TRAITS
Sometimes attribute traits interact in surprising ways. This trait is well behaved; if
you have discovered any interactions with other traits (good, bad, indifferent, etc),
please report this <https://github.com/RsrchBoy/moosex-attributeshortcuts/issues/new> so
that it can be worked around, fixed, or documented, as appropriate.
MooseX::SemiAffordanceAccessor
MooseX::SemiAffordanceAccessor changes how the "is => 'rw'" and "accessor => ..."
attribute options work. If our trait detects that an attribute has had the
MooseX::SemiAffordanceAccessor attribute trait applied, then we change our behaviour to
conform to its expectations:
• "is => 'rwp'"
This:
has foo => (is => 'rwp');
has _bar => (is => 'rwp');
...is now effectively equivalent to:
has foo => (is => 'ro', writer => '_set_foo');
has _bar => (is => 'ro', writer => '_set_bar')
• "-writer_prefix" is ignored
...as MooseX::SemiAffordanceAccessor has its own specific ideas as to how writers
should look.
SEE ALSO
Please see those modules/websites for more information related to this module.
• Moo
• MooseX::Types
• MooseX::SemiAffordanceAccessor
BUGS
Please report any bugs or feature requests on the bugtracker website
<https://github.com/RsrchBoy/moosex-attributeshortcuts/issues>
When submitting a bug or request, please include a test-file or a patch to an existing
test-file that illustrates the bug or desired feature.
AUTHOR
Chris Weyl <cweyl@alumni.drew.edu>
CONTRIBUTORS
• David Steinbrunner <dsteinbrunner@pobox.com>
• Graham Knop <haarg@haarg.org>
• Karen Etheridge <ether@cpan.org>
• Olaf Alders <olaf@wundersolutions.com>
COPYRIGHT AND LICENSE
This software is Copyright (c) 2017, 2015, 2014, 2013, 2012, 2011 by Chris Weyl.
This is free software, licensed under:
The GNU Lesser General Public License, Version 2.1, February 1999