phpman > perldoc > Moose::Manual::BestPractices(3pm)

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

VERSION
    version 2.2200

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 your 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. (This is preferred to
    placing "no Moose" at the end of your package).

    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.

  Avoid "lazy_build"
    As described above, you rarely actually need a clearer or a predicate. "lazy_build" adds both to
    your public API, which exposes you to use cases that you must now test for. It's much better to
    avoid adding them until you really need them - use explicit "lazy" and "builder" options
    instead.

  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.

AUTHORS
    *   Stevan Little <stevan AT cpan.org>

    *   Dave Rolsky <autarch AT urth.org>

    *   Jesse Luehrs <doy AT cpan.org>

    *   Shawn M Moore <sartak AT cpan.org>

    *   יובל קוג'מן (Yuval Kogman) <nothingmuch AT woobling.org>

    *   Karen Etheridge <ether AT cpan.org>

    *   Florian Ragwitz <rafl AT debian.org>

    *   Hans Dieter Pearcey <hdp AT cpan.org>

    *   Chris Prather <chris AT prather.org>

    *   Matt S Trout <mstrout AT cpan.org>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2006 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.