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

NAME
    Moose::Manual::Types - Moose's type system

VERSION
    version 2.2200

TYPES IN PERL?
    Moose provides its own type system for attributes. You can also use these types to validate
    method parameters with the help of a MooseX module.

    Moose's type system is based on a combination of Perl 5's own *implicit* types and some Perl 6
    concepts. You can create your own subtypes with custom constraints, making it easy to express
    any sort of validation.

    Types have names, and you can re-use them by name, making it easy to share types throughout a
    large application.

    However, this is not a "real" type system. Moose does not magically make Perl start associating
    types with variables. This is just an advanced parameter checking system which allows you to
    associate a name with a constraint.

    That said, it's still pretty damn useful, and we think it's one of the things that makes Moose
    both fun and powerful. Taking advantage of the type system makes it much easier to ensure that
    you are getting valid data, and it also contributes greatly to code maintainability.

THE TYPES
    The basic Moose type hierarchy looks like this

      Any
          Item
              Bool
              Maybe[`a]
              Undef
              Defined
                  Value
                      Str
                          Num
                              Int
                          ClassName
                          RoleName
                  Ref
                      ScalarRef[`a]
                      ArrayRef[`a]
                      HashRef[`a]
                      CodeRef
                      RegexpRef
                      GlobRef
                      FileHandle
                      Object

    In practice, the only difference between "Any" and "Item" is conceptual. "Item" is used as the
    top-level type in the hierarchy.

    The rest of these types correspond to existing Perl concepts. In particular:

    *   "Bool" accepts 1 for true, and undef, 0, or the empty string as false.

    *   "Maybe[`a]" accepts either "`a" or "undef".

    *   "Num" accepts integers, floating point numbers (both in decimal notation & exponential
        notation), 0, .0, 0.0 etc. It doesn't accept numbers with whitespace, Inf, Infinity, "0 but
        true", NaN & other such strings.

    *   "ClassName" and "RoleName" accept strings that are either the name of a class or the name of
        a role. The class/role must already be loaded when the constraint is checked.

    *   "FileHandle" accepts either an IO::Handle object or a builtin perl filehandle (see
        "openhandle" in Scalar::Util).

    *   "Object" accepts any blessed reference.

    The types followed by "[`a]" can be parameterized. So instead of just plain "ArrayRef" we can
    say that we want "ArrayRef[Int]" instead. We can even do something like
    "HashRef[ArrayRef[Str]]".

    The "Maybe[`a]" type deserves a special mention. Used by itself, it doesn't really mean anything
    (and is equivalent to "Item"). When it is parameterized, it means that the value is either
    "undef" or the parameterized type. So "Maybe[Int]" means an integer or "undef".

    For more details on the type hierarchy, see Moose::Util::TypeConstraints.

WHAT IS A TYPE?
    It's important to realize that types are not classes (or packages). Types are just objects
    (Moose::Meta::TypeConstraint objects, to be exact) with a name and a constraint. Moose maintains
    a global type registry that lets it convert names like "Num" into the appropriate object.

    However, class names *can be* type names. When you define a new class using Moose, it defines an
    associated type name behind the scenes:

      package MyApp::User;

      use Moose;

    Now you can use 'MyApp::User' as a type name:

      has creator => (
          is  => 'ro',
          isa => 'MyApp::User',
      );

    However, for non-Moose classes there's no magic. You may have to explicitly declare the class
    type. This is a bit muddled because Moose assumes that any unknown type name passed as the "isa"
    value for an attribute is a class. So this works:

      has 'birth_date' => (
          is  => 'ro',
          isa => 'DateTime',
      );

    In general, when Moose is presented with an unknown name, it assumes that the name is a class:

      subtype 'ModernDateTime'
          => as 'DateTime'
          => where { $_->year() >= 1980 }
          => message { 'The date you provided is not modern enough' };

      has 'valid_dates' => (
          is  => 'ro',
          isa => 'ArrayRef[DateTime]',
      );

    Moose will assume that "DateTime" is a class name in both of these instances.

SUBTYPES
    Moose uses subtypes in its built-in hierarchy. For example, "Int" is a child of "Num".

    A subtype is defined in terms of a parent type and a constraint. Any constraints defined by the
    parent(s) will be checked first, followed by constraints defined by the subtype. A value must
    pass *all* of these checks to be valid for the subtype.

    Typically, a subtype takes the parent's constraint and makes it more specific.

    A subtype can also define its own constraint failure message. This lets you do things like have
    an error "The value you provided (20), was not a valid rating, which must be a number from
    1-10." This is much friendlier than the default error, which just says that the value failed a
    validation check for the type. The default error can, however, be made more friendly by
    installing Devel::PartialDump (version 0.14 or higher), which Moose will use if possible to
    display the invalid value.

    Here's a simple (and useful) subtype example:

      subtype 'PositiveInt',
          as 'Int',
          where { $_ > 0 },
          message { "The number you provided, $_, was not a positive number" };

    Note that the sugar functions for working with types are all exported by
    Moose::Util::TypeConstraints.

TYPE NAMES
    Type names are global throughout the current Perl interpreter. Internally, Moose maps names to
    type objects via a registry.

    If you have multiple apps or libraries all using Moose in the same process, you could have
    problems with collisions. We recommend that you prefix names with some sort of namespace
    indicator to prevent these sorts of collisions.

    For example, instead of calling a type "PositiveInt", call it "MyApp::Type::PositiveInt" or
    "MyApp::Types::PositiveInt". We recommend that you centralize all of these definitions in a
    single package, "MyApp::Types", which can be loaded by other classes in your application.

    However, before you do this, you should look at the MooseX::Types module. This module makes it
    easy to create a "type library" module, which can export your types as perl constants.

      has 'counter' => (is => 'rw', isa => PositiveInt);

    This lets you use a short name rather than needing to fully qualify the name everywhere. It also
    allows you to easily create parameterized types:

      has 'counts' => (is => 'ro', isa => HashRef[PositiveInt]);

    This module will check your names at compile time, and is generally more robust than the string
    type parsing for complex cases.

COERCION
    A coercion lets you tell Moose to automatically convert one type to another.

      subtype 'ArrayRefOfInts',
          as 'ArrayRef[Int]';

      coerce 'ArrayRefOfInts',
          from 'Int',
          via { [ $_ ] };

    You'll note that we created a subtype rather than coercing "ArrayRef[Int]" directly. It's a bad
    idea to add coercions to the raw built in types.

    Coercions are global, just like type names, so a coercion applied to a built in type is seen by
    all modules using Moose types. This is *another* reason why it is good to namespace your types.

    Moose will *never* try to coerce a value unless you explicitly ask for it. This is done by
    setting the "coerce" attribute option to a true value:

      package Foo;

      has 'sizes' => (
          is     => 'ro',
          isa    => 'ArrayRefOfInts',
          coerce => 1,
      );

      Foo->new( sizes => 42 );

    This code example will do the right thing, and the newly created object will have "[ 42 ]" as
    its "sizes" attribute.

  Deep coercion
    Deep coercion is the coercion of type parameters for parameterized types. Let's take these types
    as an example:

      subtype 'HexNum',
          as 'Str',
          where { /[a-f0-9]/i };

      coerce 'Int',
          from 'HexNum',
          via { hex $_ };

      has 'sizes' => (
          is     => 'ro',
          isa    => 'ArrayRef[Int]',
          coerce => 1,
      );

    If we try passing an array reference of hex numbers for the "sizes" attribute, Moose will not do
    any coercion.

    However, you can define a set of subtypes to enable coercion between two parameterized types.

      subtype 'ArrayRefOfHexNums',
          as 'ArrayRef[HexNum]';

      subtype 'ArrayRefOfInts',
          as 'ArrayRef[Int]';

      coerce 'ArrayRefOfInts',
          from 'ArrayRefOfHexNums',
          via { [ map { hex } @{$_} ] };

      Foo->new( sizes => [ 'a1', 'ff', '22' ] );

    Now Moose will coerce the hex numbers to integers.

    Moose does not attempt to chain coercions, so it will not coerce a single hex number. To do
    that, we need to define a separate coercion:

      coerce 'ArrayRefOfInts',
          from 'HexNum',
          via { [ hex $_ ] };

    Yes, this can all get verbose, but coercion is tricky magic, and we think it's best to make it
    explicit.

TYPE UNIONS
    Moose allows you to say that an attribute can be of two or more disparate types. For example, we
    might allow an "Object" or "FileHandle":

      has 'output' => (
          is  => 'rw',
          isa => 'Object | FileHandle',
      );

    Moose actually parses that string and recognizes that you are creating a type union. The
    "output" attribute will accept any sort of object, as well as an unblessed file handle. It is up
    to you to do the right thing for each of them in your code.

    Whenever you use a type union, you should consider whether or not coercion might be a better
    answer.

    For our example above, we might want to be more specific, and insist that output be an object
    with a "print" method:

      duck_type 'CanPrint', [qw(print)];

    We can coerce file handles to an object that satisfies this condition with a simple wrapper
    class:

      package FHWrapper;

      use Moose;

      has 'handle' => (
          is  => 'rw',
          isa => 'FileHandle',
      );

      sub print {
          my $self = shift;
          my $fh   = $self->handle();

          print {$fh} @_;
      }

    Now we can define a coercion from "FileHandle" to our wrapper class:

      coerce 'CanPrint'
          => from 'FileHandle'
          => via { FHWrapper->new( handle => $_ ) };

      has 'output' => (
          is     => 'rw',
          isa    => 'CanPrint',
          coerce => 1,
      );

    This pattern of using a coercion instead of a type union will help make your class internals
    simpler.

TYPE CREATION HELPERS
    The Moose::Util::TypeConstraints module exports a number of helper functions for creating
    specific kinds of types. These include "class_type", "role_type", "maybe_type", and "duck_type".
    See the docs for details.

    One helper worth noting is "enum", which allows you to create a subtype of "Str" that only
    allows the specified values:

      enum 'RGB', [qw( red green blue )];

    This creates a type named "RGB".

ANONYMOUS TYPES
    All of the type creation functions return a type object. This type object can be used wherever
    you would use a type name, as a parent type, or as the value for an attribute's "isa" option:

      has 'size' => (
          is  => 'ro',
          isa => subtype( 'Int' => where { $_ > 0 } ),
      );

    This is handy when you want to create a one-off type and don't want to "pollute" the global
    namespace registry.

VALIDATING METHOD PARAMETERS
    Moose does not provide any means of validating method parameters. However, there are several
    MooseX extensions on CPAN which let you do this.

    The simplest and least sugary is Params::ValidationCompiler. This lets you validate a set of
    named parameters using Moose types:

      use Moose::Util::TypeConstraints qw( find_type_constraint );
      use Params::ValidationCompiler qw( validation_for );

      {
          my $validator = validation_for(
              params => {
                  foo => { type => find_type_constraint('Int') },
                  bar => {
                      type     => find_type_constraint('Str'),
                      optional => 1,
                  },
                  baz => {
                      type    => find_type_constraint('Int'),
                      default => 42,
                  },
              },
          );

          sub foo {
              my %args = $validator->(@_);
          }
    }

    Params::ValidationCompiler also supports coercions.

    There are several more powerful extensions that support method parameter validation using Moose
    types, including Moops, which gives you a full-blown "method" keyword.

      method morning ( Str $name ) {
          $self->say("Good morning ${name}!");
      }

LOAD ORDER ISSUES
    Because Moose types are defined at runtime, you may run into load order problems. In particular,
    you may want to use a class's type constraint before that type has been defined.

    In order to ameliorate this problem, we recommend defining *all* of your custom types in one
    module, "MyApp::Types", and then loading this module in all of your other modules.

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.