Moose::Manual::BestPraUsereContributed Perl DMoose::Manual::BestPractices(3pm)NAMEMoose::Manual::BestPractices - Get the most out of Moose
VERSION
version 2.2009
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.little@iinteractive.com>
· Dave Rolsky <autarch@urth.org>
· Jesse Luehrs <doy@tozt.net>
· Shawn M Moore <code@sartak.org>
· יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
· Karen Etheridge <ether@cpan.org>
· Florian Ragwitz <rafl@debian.org>
· Hans Dieter Pearcey <hdp@weftsoar.net>
· Chris Prather <chris@prather.org>
· Matt S Trout <mst@shadowcat.co.uk>
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.
perl v5.26.1 2017-12-21 Moose::Manual::BestPractices(3pm)
