Provided by: libmoosex-attributeshortcuts-perl_0.037-2_all bug

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