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

SYNOPSIS
    The following is example usage for this module.

        package MyApp::MyClass;
            
    use Moose;
        use MooseX::Types::Moose qw(Str Int);
        use MooseX::Types::Structured qw(Dict Tuple);

        has name => (isa=>Dict[first_name=>Str, last_name=>Str]);

    Then you can instantiate this class with something like:

        my $instance = MyApp::MyClass->new(
                    name=>{first_name=>'John', last_name=>'Napiorkowski'},
            );

    But all of these would cause an error:

        my $instance = MyApp::MyClass->new(name=>'John');
        my $instance = MyApp::MyClass->new(name=>{first_name=>'John'});
        my $instance = MyApp::MyClass->new(name=>{first_name=>'John', age=>39});

    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 explicitely name all the allow type constraints inside the
    structure. The generalized form is:

        TypeConstraint[TypeParameters]

    Where TypeParameters is a list of type constraints.

    This type library enables structured type constraints. These work in a
    similar way to parameterized constraints that are built into the core
    Moose types, except that you are allowed to define the container's
    entire structure. For example, you could define a parameterized
    constraint like so:

        subtype HashOfInts,
         as Hashref[Int];

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

        subtype StringFollowedByInt,
         as Tuple[Str,Int];

    would constrain it's value to something like ['hello', 111];

    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

    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;
        
    has $_ for qw(name age);
        
    package MyApp::MyClass;
        use Moose;
        
    has person => (isa=>'MyApp::MyStruct');             
        
    my $instance = MyApp::MyClass->new(
            person=>MyApp::MyStruct->new(name=>'John', age=>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:

        subtype 'MyStruct',
         as 'MyApp::MyStruct';
        
    coerce 'MyStruct',
         from (Dict[name=>Str, age=>Int]),
         via {
            MyApp::MyStruct->new(%$_);
         },
         from (Dict[last_name=>Str, first_name=>Str, dob=>DateTime]),
         via {
            my $name = $_->{first_name} .' '. $_->{last_name};
            my $age = DateTime->now - $_->{dob};
            MyApp::MyStruct->new(
            name=>$name,
            age=>$age->years );
         };

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

        subtype Person,
         as Dict[name=>Str, age=>iIt];
             
    subtype FriendlyPerson,
         as Person[name=>Str, age=>Int, totalFriends=>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 probably clarify how this works at a future
    point, so it's recommended to avoid (should not realy be needed so much
    anyway). For now this is supported in an EXPERIMENTAL way. In the future
    we will probably clarify how to augment existing structured types.

  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,
         from BlessedPersonObject,
         via { +{name=>$_->name, age=>$_->age} },
         from ArrayRef,
         via { +{name=>$_->[0], age=>$_->[1] },
         from Dict[fullname=>Fullname, dob=>DateTime],
         via {
            my $age = $_->dob - DateTime->now;
            +{
                name=> $_->{fullname}->{first} .' '. $_->{fullname}->{last},
                age=>$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.

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 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}

SEE ALSO
    The following modules or resources may be of interest.

    Moose, MooseX::TypeLibrary, Moose::Meta::TypeConstraint,
    MooseX::Meta::TypeConstraint::Structured

TODO
    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.

