more pod updates and clarification

[gitmo/MooseX-Types-Structured.git] / lib / MooseX / Types / Structured.pm

package MooseX::Types::Structured;

use 5.008;
use Moose::Util::TypeConstraints;
use MooseX::Meta::TypeConstraint::Structured;
use MooseX::Types -declare => [qw(Dict Tuple Optional)];

our $VERSION = '0.07';
our $AUTHORITY = 'cpan:JJNAPIORK';

=head1 NAME

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

=head1 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.

=head1 DESCRIPTION

A structured type constraint is a standard container L<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 
L<Moose::Meta::TypeConstraint> objects.

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

=head2 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.

=head2 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 L<Moose> cookbook
entry L<Moose::Cookbook::Recipe5> for an explanation.  The section L</Coercions>
has additional examples and discussion.

=head2 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.

=head2 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.

=head2 Recursion

Newer versions of L<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 L<MooseX::Types> and the test cases.

=head1 TYPE CONSTRAINTS

This type library defines the following constraints.

=head2 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]

=head2 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}

=head2 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'}
    
=head1 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.

=head2 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(
        name=>'John Napiorkowski',
        age=>39,
    );
        
    __PACKAGE__->new(
        first=>'John',
        last=>'Napiorkowski',
        years=>39,
    );
    
    __PACKAGE__->new(
        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.

=cut

Moose::Util::TypeConstraints::get_type_constraint_registry->add_type_constraint(
	MooseX::Meta::TypeConstraint::Structured->new(
		name => "MooseX::Types::Structured::Tuple" ,
		parent => find_type_constraint('ArrayRef'),
		constraint_generator=> sub { 
			## Get the constraints and values to check
            my ($type_constraints, $values) = @_;
			my @type_constraints = defined $type_constraints ?
             @$type_constraints : ();            
			my @values = defined $values ? @$values: ();
			## Perform the checking
			while(@type_constraints) {
				my $type_constraint = shift @type_constraints;
				if(@values) {
					my $value = shift @values;
					unless($type_constraint->check($value)) {
						return;
					}				
				} else {
                    ## Test if the TC supports null values
					unless($type_constraint->check()) {
						return;
					}
				}
			}
			## Make sure there are no leftovers.
			if(@values) {
                warn "I failed since there were left over values";
				return;
			} elsif(@type_constraints) {
                warn "I failed due to left over TC";
				return;
			} else {
				return 1;
			}
		}
	)
);
	
Moose::Util::TypeConstraints::get_type_constraint_registry->add_type_constraint(
	MooseX::Meta::TypeConstraint::Structured->new(
		name => "MooseX::Types::Structured::Dict",
		parent => find_type_constraint('HashRef'),
		constraint_generator=> sub { 
			## Get the constraints and values to check
            my ($type_constraints, $values) = @_;
			my %type_constraints = defined $type_constraints ?
             @$type_constraints : ();            
			my %values = defined $values ? %$values: ();
			## Perform the checking
			while(%type_constraints) {
				my($key, $type_constraint) = each %type_constraints;
				delete $type_constraints{$key};
				if(exists $values{$key}) {
					my $value = $values{$key};
					delete $values{$key};
					unless($type_constraint->check($value)) {
						return;
					}
				} else {
                    ## Test to see if the TC supports null values
					unless($type_constraint->check()) {
						return;
					}
				}
			}
			## Make sure there are no leftovers.
			if(%values) { 
				return;
			} elsif(%type_constraints) {
				return;
			} else {
				return 1;
			}
		},
	)
);

OPTIONAL: {
    my $Optional = Moose::Meta::TypeConstraint::Parameterizable->new(
        name => 'MooseX::Types::Structured::Optional',
        package_defined_in => __PACKAGE__,
        parent => find_type_constraint('Item'),
        constraint => sub { 1 },
        constraint_generator => sub {
            my ($type_parameter, @args) = @_;
            my $check = $type_parameter->_compiled_type_constraint();
            return sub {
                my (@args) = @_;
                ## Does the arg exist?  Something exists if it's a 'real' value
                ## or if it is set to undef.
                if(exists($args[0])) {
                    ## If it exists, we need to validate it
                    $check->($args[0]);
                } else {
                    ## But it's is okay if the value doesn't exists
                    return 1;
                }
            }
        }
    );

    Moose::Util::TypeConstraints::register_type_constraint($Optional);
    Moose::Util::TypeConstraints::add_parameterizable_type($Optional);
}


=head1 SEE ALSO

The following modules or resources may be of interest.

L<Moose>, L<MooseX::Types>, L<Moose::Meta::TypeConstraint>,
L<MooseX::Meta::TypeConstraint::Structured>

=head1 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.

=head1 AUTHOR

John Napiorkowski, C<< <jjnapiork@cpan.org> >>

=head1 COPYRIGHT & LICENSE

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

=cut
	
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