/ 
Mouse-0.33
River stage three • 232 direct dependents • 562 total dependents
/ Mouse::Util::TypeConstraints

NAME

Mouse::Util::TypeConstraints - Type constraint system for Mouse

SYNOPSIS

use Mouse::Util::TypeConstraints;

subtype 'Natural'
    => as 'Int'
    => where { $_ > 0 };

subtype 'NaturalLessThanTen'
    => as 'Natural'
    => where { $_ < 10 }
    => message { "This number ($_) is not less than ten!" };

coerce 'Num'
    => from 'Str'
      => via { 0+$_ };

enum 'RGBColors' => qw(red green blue);

no Mouse::Util::TypeConstraints;

DESCRIPTION

This module provides Mouse with the ability to create custom type constraints to be used in attribute definition.

Important Caveat

This is NOT a type system for Perl 5. These are type constraints, and they are not used by Mouse unless you tell it to. No type inference is performed, expressions are not typed, etc. etc. etc.

A type constraint is at heart a small "check if a value is valid" function. A constraint can be associated with an attribute. This simplifies parameter validation, and makes your code clearer to read, because you can refer to constraints by name.

Slightly Less Important Caveat

It is always a good idea to quote your type names.

This prevents Perl from trying to execute the call as an indirect object call. This can be an issue when you have a subtype with the same name as a valid class.

For instance:

subtype DateTime => as Object => where { $_->isa('DateTime') };

will just work, while this:

use DateTime;
subtype DateTime => as Object => where { $_->isa('DateTime') };

will fail silently and cause many headaches. The simple way to solve this, as well as future proof your subtypes from classes which have yet to have been created, is to quote the type name:

use DateTime;
subtype 'DateTime' => as 'Object' => where { $_->isa('DateTime') };

Default Type Constraints

This module also provides a simple hierarchy for Perl 5 types, here is that hierarchy represented visually.

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

NOTE: Any type followed by a type parameter [`a] can be parameterized, this means you can say:

ArrayRef[Int]    # an array of integers
HashRef[CodeRef] # a hash of str to CODE ref mappings
Maybe[Str]       # value may be a string, may be undefined

If Mouse finds a name in brackets that it does not recognize as an existing type, it assumes that this is a class name, for example ArrayRef[DateTime].

NOTE: Unless you parameterize a type, then it is invalid to include the square brackets. I.e. ArrayRef[] will be treated as a new type name, not as a parameterization of ArrayRef.

NOTE: The Undef type constraint for the most part works correctly now, but edge cases may still exist, please use it sparingly.

NOTE: The ClassName type constraint does a complex package existence check. This means that your class must be loaded for this type constraint to pass.

NOTE: The RoleName constraint checks a string is a package name which is a role, like 'MyApp::Role::Comparable'. The Role constraint checks that an object does the named role.

Type Constraint Naming

Type name declared via this module can only contain alphanumeric characters, colons (:), and periods (.).

Since the types created by this module are global, it is suggested that you namespace your types just as you would namespace your modules. So instead of creating a Color type for your My::Graphics module, you would call the type My::Graphics::Types::Color instead.

Use with Other Constraint Modules

This module can play nicely with other constraint modules with some slight tweaking. The where clause in types is expected to be a CODE reference which checks it's first argument and returns a boolean. Since most constraint modules work in a similar way, it should be simple to adapt them to work with Mouse.

For instance, this is how you could use it with Declare::Constraints::Simple to declare a completely new type.

type 'HashOfArrayOfObjects',
    {
    where => IsHashRef(
        -keys   => HasLength,
        -values => IsArrayRef(IsObject)
    )
};

Here is an example of using Test::Deep and it's non-test related eq_deeply function.

type 'ArrayOfHashOfBarsAndRandomNumbers'
    => where {
        eq_deeply($_,
            array_each(subhashof({
                bar           => isa('Bar'),
                random_number => ignore()
            })))
      };

METHODS

optimized_constraints -> HashRef[CODE]

Returns the simple type constraints that Mouse understands.

FUNCTIONS

subtype 'Name' = as 'Parent' => where { } ...>
subtype as 'Parent' = where { } ...>
class_type ($class, ?$options)
role_type ($role, ?$options)
enum (\@values)

THANKS

Much of this documentation was taken from Moose::Util::TypeConstraints