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Moose::Manual::Types(3pm) User Contributed Perl Documentation 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:
o "Bool" accepts 1 for true, and undef, 0, or the empty string as false.
o "Maybe[`a]" accepts either "`a" or "undef".
o "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.
o "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.
o "FileHandle" accepts either an IO::Handle object or a builtin perl filehandle (see
"openhandle" in Scalar::Util).
o "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
o Stevan Little <stevan AT cpan.org>
o Dave Rolsky <autarch AT urth.org>
o Jesse Luehrs <doy AT cpan.org>
o Shawn M Moore <sartak AT cpan.org>
o ' (Yuval Kogman) <nothingmuch AT woobling.org>
o Karen Etheridge <ether AT cpan.org>
o Florian Ragwitz <rafl AT debian.org>
o Hans Dieter Pearcey <hdp AT cpan.org>
o Chris Prather <chris AT prather.org>
o 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.
perl v5.34.0 2022-02-06 Moose::Manual::Types(3pm)
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On Apache
Under GNU General Public License
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