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Moose::Manual::BestPractices(3)      User Contributed Perl Documentation     Moose::Manual::BestPractices(3)



NAME
       Moose::Manual::BestPractices - Get the most out of Moose

VERSION
       version 2.0205

RECOMMENDATIONS
       Moose has a lot of features, and there's definitely more than one way to do it. However, we think
       that picking a subset of these features and using them consistently makes everyone's life easier.

       Of course, as with any list of "best practices", these are really just opinions. Feel free to ignore
       us.

   "namespace::autoclean" and immutabilize
       We recommend that you remove the Moose sugar and end your Moose class definitions by making your
       class immutable.

         package Person;

         use Moose;
         use namespace::autoclean;

         # extends, roles, attributes, etc.

         # methods

         __PACKAGE__->meta->make_immutable;

         1;

       The "use namespace::autoclean" bit is simply good code hygiene, as it removes imported symbols from
       you class's namespace at the end of your package's compile cycle, including Moose keywords.  Once the
       class has been built, these keywords are not needed.

       The "make_immutable" call allows Moose to speed up a lot of things, most notably object construction.
       The trade-off is that you can no longer change the class definition.

   Never override "new"
       Overriding "new" is a very bad practice. Instead, you should use a "BUILD" or "BUILDARGS" methods to
       do the same thing. When you override "new", Moose can no longer inline a constructor when your class
       is immutabilized.

       There are two good reasons to override "new". One, you are writing a MooseX extension that provides
       its own Moose::Object subclass and a subclass of Moose::Meta::Method::Constructor to inline the
       constructor. Two, you are subclassing a non-Moose parent.

       If you know how to do that, you know when to ignore this best practice ;)

   Always call the original/parent "BUILDARGS"
       If you "override" the "BUILDARGS" method in your class, make sure to play nice and call "super()" to
       handle cases you're not checking for explicitly.

       The default "BUILDARGS" method in Moose::Object handles both a list and hashref of named parameters
       correctly, and also checks for a non-hashref single argument.

   Provide defaults whenever possible, otherwise use "required"
       When your class provides defaults, this makes constructing new objects simpler. If you cannot provide
       a default, consider making the attribute "required".

       If you don't do either, an attribute can simply be left unset, increasing the complexity of your
       object, because it has more possible states that you or the user of your class must account for.

   Use "builder" instead of "default" most of the time
       Builders can be inherited, they have explicit names, and they're just plain cleaner.

       However, do use a default when the default is a non-reference, or when the default is simply an empty
       reference of some sort.

       Also, keep your builder methods private.

   Be "lazy"
       Lazy is good, and often solves initialization ordering problems. It's also good for deferring work
       that may never have to be done. Make your attributes "lazy" unless they're "required" or have trivial
       defaults.

   Consider keeping clearers and predicates private
       Does everyone really need to be able to clear an attribute?  Probably not. Don't expose this
       functionality outside your class by default.

       Predicates are less problematic, but there's no reason to make your public API bigger than it has to
       be.

   Default to read-only, and consider keeping writers private
       Making attributes mutable just means more complexity to account for in your program. The alternative
       to mutable state is to encourage users of your class to simply make new objects as needed.

       If you must make an attribute read-write, consider making the writer a separate private method.
       Narrower APIs are easy to maintain, and mutable state is trouble.

       In order to declare such attributes, provide a private "writer" parameter:

           has pizza => (
               is     => 'ro',
               isa    => 'Pizza',
               writer => '_pizza',
           );

   Think twice before changing an attribute's type in a subclass
       Down this path lies great confusion. If the attribute is an object itself, at least make sure that it
       has the same interface as the type of object in the parent class.

   Don't use the "initializer" feature
       Don't know what we're talking about? That's fine.

   Use Moose::Meta::Attribute::Native traits instead of "auto_deref"
       The "auto_deref" feature is a bit troublesome. Directly exposing a complex attribute is ugly.
       Instead, consider using Moose::Meta::Attribute::Native traits to define an API that only exposes the
       necessary pieces of functionality.

   Always call "inner" in the most specific subclass
       When using "augment" and "inner", we recommend that you call "inner" in the most specific subclass of
       your hierarchy. This makes it possible to subclass further and extend the hierarchy without changing
       the parents.

   Namespace your types
       Use some sort of namespacing convention for type names. We recommend something like
       "MyApp::Type::Foo". We also recommend considering MooseX::Types.

   Do not coerce Moose built-ins directly
       If you define a coercion for a Moose built-in like "ArrayRef", this will affect every application in
       the Perl interpreter that uses this type.

           # very naughty!
           coerce 'ArrayRef'
               => from Str
               => via { [ split /,/ ] };

       Instead, create a subtype and coerce that:

           subtype 'My::ArrayRef' => as 'ArrayRef';

           coerce 'My::ArrayRef'
               => from 'Str'
               => via { [ split /,/ ] };

   Do not coerce class names directly
       Just as with Moose built-in types, a class type is global for the entire interpreter. If you add a
       coercion for that class name, it can have magical side effects elsewhere:

           # also very naughty!
           coerce 'HTTP::Headers'
               => from 'HashRef'
               => via { HTTP::Headers->new( %{$_} ) };

       Instead, we can create an "empty" subtype for the coercion:

           subtype 'My::HTTP::Headers' => as class_type('HTTP::Headers');

           coerce 'My::HTTP::Headers'
               => from 'HashRef'
               => via { HTTP::Headers->new( %{$_} ) };

   Use coercion instead of unions
       Consider using a type coercion instead of a type union. This was covered in Moose::Manual::Types.

   Define all your types in one module
       Define all your types and coercions in one module. This was also covered in Moose::Manual::Types.

BENEFITS OF BEST PRACTICES
       Following these practices has a number of benefits.

       It helps ensure that your code will play nice with others, making it more reusable and easier to
       extend.

       Following an accepted set of idioms will make maintenance easier, especially when someone else has to
       maintain your code. It will also make it easier to get support from other Moose users, since your
       code will be easier to digest quickly.

       Some of these practices are designed to help Moose do the right thing, especially when it comes to
       immutabilization. This means your code will be faster when immutabilized.

       Many of these practices also help get the most out of meta programming. If you used an overridden
       "new" to do type coercion by hand, rather than defining a real coercion, there is no introspectable
       metadata. This sort of thing is particularly problematic for MooseX extensions which rely on
       introspection to do the right thing.

AUTHOR
       Stevan Little <stevan@iinteractive.com>

COPYRIGHT AND LICENSE
       This software is copyright (c) 2011 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 v5.12.5                                     2011-09-06                  Moose::Manual::BestPractices(3)