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MooseX-Types-Structured-0.13
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/ MooseX::Types::Structured

NAME

MooseX::Types::Structured - Structured Type Constraints for Moose

SYNOPSIS

The following is example usage for this module.

    package Person;
	
    use Moose;
    use MooseX::Types::Moose qw(Str Int HashRef);
    use MooseX::Types::Structured qw(Dict Tuple Optional);

    ## A name has a first and last part, but middle names are not required
    has name => (
        isa=>Dict[
            first => Str,
            last => Str,
            middle => Optional[Str],
        ],
    );
    
    ## description is a string field followed by a HashRef of tagged data.
    has description => (
      isa=>Tuple[
        Str,
        Optional[HashRef],
     ],
    );

Then you can instantiate this class with something like:

my $john = Person->new(
    name => {
        first => 'John',
        middle => 'James'
        last => 'Napiorkowski',
    },
    description => [
        'A cool guy who loves Perl and Moose.', {
            married_to => 'Vanessa Li',
            born_in => 'USA',
        };
    ]
);

Or with:

my $vanessa = Person->new(
    name => {
        first => 'Vanessa',
        last => 'Li'
    },
    description => ['A great student!'],
);

But all of these would cause a constraint error for the 'name' attribute:

## Value for 'name' not a HashRef
Person->new( name => 'John' );

## Value for 'name' has incorrect hash key and missing required keys
Person->new( name => {
    first_name => 'John'
});

## Also incorrect keys
Person->new( name => {
    first_name => 'John',
    age => 39,
});

## key 'middle' incorrect type, should be a Str not a ArrayRef
Person->new( name => {
    first => 'Vanessa',
    middle => [1,2],
    last => 'Li',
});

And these would cause a constraint error for the 'description' attribute:

## Should be an ArrayRef
Person->new( description => 'Hello I am a String' );

## First element must be a string not a HashRef.
Person->new (description => [{
    tag1 => 'value1',
    tag2 => 'value2'
}]);

Please see the test cases for more examples.

DESCRIPTION

A structured type constraint is a standard container Moose type constraint, such as an ArrayRef or HashRef, which has been enhanced to allow you to explicitly name all the allowed type constraints inside the structure. The generalized form is:

TypeConstraint[@TypeParameters or %TypeParameters]

Where 'TypeParameters' is an array reference or hash references of Moose::Meta::TypeConstraint objects.

This type library enables structured type constraints. It is built on top of the MooseX::Types library system, so you should review the documentation for that if you are not familiar with it.

Comparing Parameterized types to Structured types

Parameterized constraints are built into core Moose and you are probably already familar with the type constraints 'HashRef' and 'ArrayRef'. Structured types have similar functionality, so their syntax is likewise similar. For example, you could define a parameterized constraint like:

subtype ArrayOfInts,
 as Arrayref[Int];

which would constrain a value to something like [1,2,3,...] and so on. On the other hand, a structured type constraint explicitly names all it's allowed 'internal' type parameter constraints. For the example:

    subtype StringFollowedByInt,
     as Tuple[Str,Int];

would constrain it's value to things like ['hello', 111] but ['hello', 'world'] would fail, as well as ['hello', 111, 'world'] and so on. Here's another example:

subtype StringIntOptionalHashRef,
 as Tuple[
    Str, Int,
    Optional[HashRef]
 ];

This defines a type constraint that validates values like:

['Hello', 100, {key1 => 'value1', key2 => 'value2'}];
['World', 200];

Notice that the last type constraint in the structure is optional. This is enabled via the helper Optional type constraint, which is a variation of the core Moose type constraint 'Maybe'. The main difference is that Optional type constraints are required to validate if they exist, while 'Maybe' permits undefined values. So the following example would not validate:

StringIntOptionalHashRef->validate(['Hello Undefined', 1000, undef]);

Please note the subtle difference between undefined and null. If you wish to allow both null and undefined, you should use the core Moose 'Maybe' type constraint instead:

use MooseX::Types -declare [qw(StringIntMaybeHashRef)];
use MooseX::Types::Moose qw(Maybe);
use MooseX::Types::Structured qw(Tuple);

subtype StringIntMaybeHashRef,
 as Tuple[
    Str, Int, Maybe[HashRef]
 ];

This would validate the following:

['Hello', 100, {key1 => 'value1', key2 => 'value2'}];
['World', 200, undef];    
['World', 200];

Structured constraints are not limited to arrays. You can define a structure against a HashRef with 'Dict' as in this example:

subtype FirstNameLastName,
 as Dict[
    firstname => Str,
    lastname => Str,
 ];

This would constrain a HashRef to something like:

{firstname => 'Christopher', lastname= > 'Parsons'};

but all the following would fail validation:

## Incorrect keys
{first => 'Christopher', last => 'Parsons'};

## Too many keys
{firstname => 'Christopher', lastname => 'Parsons', middlename => 'Allen'};

## Not a HashRef
['Christopher', 'Christopher'];

These structures can be as simple or elaborate as you wish. You can even combine various structured, parameterized and simple constraints all together:

    subtype Crazy,
     as Tuple[
        Int,
        Dict[name=>Str, age=>Int],
        ArrayRef[Int]
     ];

Which would match "[1, {name=>'John', age=>25},[10,11,12]]". Please notice how the type parameters can be visually arranged to your liking and to improve the clarity of your meaning. You don't need to run then altogether onto a single line.

Alternatives

You should exercise some care as to whether or not your complex structured constraints would be better off contained by a real object as in the following example:

    package MyApp::MyStruct;
    use Moose;
    
    ## lazy way to make a bunch of attributes
    has $_ for qw(full_name age_in_years);
    
    package MyApp::MyClass;
    use Moose;
    
    has person => (isa => 'MyApp::MyStruct');		
    
    my $instance = MyApp::MyClass->new(
        person=>MyApp::MyStruct->new(
            full_name => 'John',
            age_in_years => 39,
        ),
    );

This method may take some additional time to setup but will give you more flexibility. However, structured constraints are highly compatible with this method, granting some interesting possibilities for coercion. Try:

package MyApp::MyClass;

use Moose;
use MyApp::MyStruct;

## It's recommended your type declarations live in a separate class in order
## to promote reusability and clarity.  Inlined here for brevity.

use MooseX::Types::DateTime qw(DateTime);
use MooseX::Types -declare [qw(MyStruct)];
use MooseX::Types::Moose qw(Str Int);
use MooseX::Types::Structured qw(Dict);

## Use class_type to create an ISA type constraint if your object doesn't
## inherit from Moose::Object.
class_type 'MyApp::MyStruct';

## Just a shorter version really.
subtype MyStruct,
 as 'MyApp::MyStruct';

## Add the coercions.
coerce MyStruct,
 from Dict[
    full_name=>Str,
    age_in_years=>Int
 ], via {
    MyApp::MyStruct->new(%$_);
 },
 from Dict[
    lastname=>Str,
    firstname=>Str,
    dob=>DateTime
 ], via {
    my $name = $_->{firstname} .' '. $_->{lastname};
    my $age = DateTime->now - $_->{dob};
    
    MyApp::MyStruct->new(
        full_name=>$name,
        age_in_years=>$age->years,
    );
 };
 
has person => (isa=>MyStruct);

This would allow you to instantiate with something like:

my $obj = MyApp::MyClass->new( person => {
    full_name=>'John Napiorkowski',
    age_in_years=>39,
});

Or even:

my $obj = MyApp::MyClass->new( person => {
    lastname=>'John',
    firstname=>'Napiorkowski',
    dob=>DateTime->new(year=>1969),
});

If you are not familiar with how coercions work, check out the Moose cookbook entry Moose::Cookbook::Recipe5 for an explanation. The section "Coercions" has additional examples and discussion.

Subtyping a Structured type constraint

You need to exercise some care when you try to subtype a structured type as in this example:

    subtype Person,
     as Dict[name => Str];
	 
    subtype FriendlyPerson,
     as Person[
        name => Str,
        total_friends => Int,
     ];

This will actually work BUT you have to take care that the subtype has a structure that does not contradict the structure of it's parent. For now the above works, but I will clarify the syntax for this at a future point, so it's recommended to avoid (should not really be needed so much anyway). For now this is supported in an EXPERIMENTAL way. Your thoughts, test cases and patches are welcomed for discussion. If you find a good use for this, please let me know.

Coercions

Coercions currently work for 'one level' deep. That is you can do:

    subtype Person,
     as Dict[
        name => Str,
        age => Int
    ];
    
    subtype Fullname,
     as Dict[
        first => Str,
        last => Str
     ];
    
    coerce Person,
     ## Coerce an object of a particular class
     from BlessedPersonObject, via {
        +{
            name=>$_->name,
            age=>$_->age,
        };
     },
     
     ## Coerce from [$name, $age]
     from ArrayRef, via {
        +{
            name=>$_->[0],
            age=>$_->[1],
        },
     },
     ## Coerce from {fullname=>{first=>...,last=>...}, dob=>$DateTimeObject}
     from Dict[fullname=>Fullname, dob=>DateTime], via {
        my $age = $_->dob - DateTime->now;
        my $firstn = $_->{fullname}->{first};
        my $lastn = $_->{fullname}->{last}
        +{
            name => $_->{fullname}->{first} .' '. ,
            age =>$age->years
        }
     };

And that should just work as expected. However, if there are any 'inner' coercions, such as a coercion on 'Fullname' or on 'DateTime', that coercion won't currently get activated.

Please see the test '07-coerce.t' for a more detailed example. Discussion on extending coercions to support this welcome on the Moose development channel or mailing list.

Recursion

Newer versions of MooseX::Types support recursive type constraints. That is you can include a type constraint as a contained type constraint of itself. For example:

subtype Person,
 as Dict[
 	name=>Str,
 	friends=>Optional[
 		ArrayRef[Person]
 	],
 ];

This would declare a Person subtype that contains a name and an optional ArrayRef of Persons who are friends as in:

{
	name => 'Mike',
	friends => [
		{ name => 'John' },
		{ name => 'Vincent' },
		{
			name => 'Tracey',
			friends => [
				{ name => 'Stephenie' },
				{ name => 'Ilya' },
			],
		},
	],
};

Please take care to make sure the recursion node is either Optional, or declare a Union with an non recursive option such as:

subtype Value
 as Tuple[
 	Str,
 	Str|Tuple,
 ];

Which validates:

[
	'Hello', [
		'World', [
			'Is', [
				'Getting',
				'Old',
			],
		],
	],
];

Otherwise you will define a subtype thatis impossible to validate since it is infinitely recursive. For more information about defining recursive types, please see the documentation in MooseX::Types and the test cases.

TYPE CONSTRAINTS

This type library defines the following constraints.

Tuple[@constraints]

This defines an ArrayRef based constraint which allows you to validate a specific list of contained constraints. For example:

Tuple[Int,Str]; ## Validates [1,'hello']
Tuple[Str|Object, Int]; ## Validates ['hello', 1] or [$object, 2]

Dict[%constraints]

This defines a HashRef based constraint which allowed you to validate a specific hashref. For example:

Dict[name=>Str, age=>Int]; ## Validates {name=>'John', age=>39}

Optional[$constraint]

This is primarily a helper constraint for Dict and Tuple type constraints. What this allows if for you to assert that a given type constraint is allowed to be null (but NOT undefined). If the value is null, then the type constraint passes but if the value is defined it must validate against the type constraint. This makes it easy to make a Dict where one or more of the keys doesn't have to exist or a tuple where some of the values are not required. For example:

subtype Name() => as Dict[
    first=>Str,
    last=>Str,
    middle=>Optional[Str],
];

Creates a constraint that validates against a hashref with the keys 'first' and 'last' being strings and required while an optional key 'middle' is must be a string if it appears but doesn't have to appear. So in this case both the following are valid:

{first=>'John', middle=>'James', last=>'Napiorkowski'}
{first=>'Vanessa', last=>'Li'}

EXPORTABLE SUBROUTINES

This type library makes available for export the following subroutines

slurpy

Structured type constraints by their nature are closed; that is validation will depend on an exact match between your structure definition and the arguments to be checked. Sometimes you might wish for a slightly looser amount of validation. For example, you may wish to validate the first 3 elements of an array reference and allow for an arbitrary number of additional elements. At first thought you might think you could do it this way:

#  I want to validate stuff like: [1,"hello", $obj, 2,3,4,5,6,...]
subtype AllowTailingArgs,
 as Tuple[
   Int,
   Str,
   Object,
   ArrayRef[Int],
 ];

However what this will actually validate are structures like this:

[10,"Hello", $obj, [11,12,13,...] ]; # Notice element 4 is an ArrayRef

In order to allow structured validation of, "and then some", arguments, you can use the </slurpy> method against a type constraint. For example:

use MooseX::Types::Structured qw(Tuple slurpy);

subtype AllowTailingArgs,
 as Tuple[
   Int,
   Str,
   Object,
   slurpy ArrayRef[Int],
 ];

This will now work as expected, validating ArrayRef structures such as:

[1,"hello", $obj, 2,3,4,5,6,...]

A few caveats apply. First, the slurpy type constraint must be the last one in the list of type constraint parameters. Second, the parent type of the slurpy type constraint must match that of the containing type constraint. That means that a Tuple can allow a slurpy ArrayRef (or children of ArrayRefs, including another Tuple) and a Dict can allow a slurpy HashRef (or children/subtypes of HashRef, also including other Dict constraints).

Please note the the technical way this works 'under the hood' is that the slurpy keywork transforms the target type constraint into a coderef. Please do not try to create your own custom coderefs; always use the slurpy method. The underlying technology may change in the future but the slurpy keyword will be supported.

ERROR MESSAGES

Error reporting has been improved to return more useful debugging messages. Now I will stringify the incoming check value with Devel::PartialDump so that you can see the actual structure that is tripping up validation. Also, I report the 'internal' validation error, so that if a particular element inside the Structured Type is failing validation, you will see that. There's a limit to how deep this internal reporting goes, but you shouldn't see any of the "failed with ARRAY(XXXXXX)" that we got with earlier versions of this module.

This support is continuing to expand, so it's best to use these messages for debugging purposes and not for creating messages that 'escape into the wild' such as error messages sent to the user.

Please see the test '12-error.t' for a more lengthy example. Your thoughts and preferable tests or code patches very welcome!

EXAMPLES

Here are some additional example usage for structured types. All examples can be found also in the 't/examples.t' test. Your contributions are also welcomed.

Normalize a HashRef

You need a hashref to conform to a canonical structure but are required accept a bunch of different incoming structures. You can normalize using the Dict type constraint and coercions. This example also shows structured types mixed which other MooseX::Types libraries.

package Test::MooseX::Meta::TypeConstraint::Structured::Examples::Normalize;

use Moose;
use DateTime;

use MooseX::Types::Structured qw(Dict Tuple);
use MooseX::Types::DateTime qw(DateTime);
use MooseX::Types::Moose qw(Int Str Object);
use MooseX::Types -declare => [qw(Name Age Person)];
 
subtype Person,
 as Dict[
 	name=>Str,
 	age=>Int,
 ];

coerce Person,
 from Dict[
 	first=>Str, 
 	last=>Str, 
 	years=>Int,
 ], via { +{
    name => "$_->{first} $_->{last}",
    age => $_->{years},
 }},
 from Dict[
 	fullname=>Dict[
 		last=>Str, 
 		first=>Str,
 	], 
 	dob=>DateTime,
 ],
 ## DateTime needs to be inside of single quotes here to disambiguate the
 ## class package from the DataTime type constraint imported via the
 ## line "use MooseX::Types::DateTime qw(DateTime);"
 via { +{
    name => "$_->{fullname}{first} $_->{fullname}{last}",
    age => ($_->{dob} - 'DateTime'->now)->years,
 }};
 
has person => (is=>'rw', isa=>Person, coerce=>1);

And now you can instantiate with all the following:

__PACKAGE__->new(
    person=>{
        name=>'John Napiorkowski',
        age=>39,            
    },
);
    
__PACKAGE__->new(
    person=>{
        first=>'John',
        last=>'Napiorkowski',
        years=>39,
    },
);

__PACKAGE__->new(
    person=>{
        fullname => {
            first=>'John',
            last=>'Napiorkowski'
        },
        dob => 'DateTime'->new(
            year=>1969,
            month=>2,
            day=>13
        ),            
    },
);

This technique is a way to support various ways to instantiate your class in a clean and declarative way.

SEE ALSO

The following modules or resources may be of interest.

Moose, MooseX::Types, Moose::Meta::TypeConstraint, MooseX::Meta::TypeConstraint::Structured

TODO

Here's a list of stuff I would be happy to get volunteers helping with:

All POD examples need test cases in t/documentation/*.t Want to break out the examples section to a separate cookbook style POD. Want more examples and best practice / usage guidance for authors Need to clarify deep coercions, Need to clarify subtypes of subtypes.

AUTHOR

John Napiorkowski, <jjnapiork@cpan.org>

COPYRIGHT & LICENSE

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.