NAME

       MooX::Struct - make simple lightweight record-like structures that make sounds like cows

SYNOPSIS

        use MooX::Struct
           Point   => [ 'x', 'y' ],
           Point3D => [ -extends => ['Point'], 'z' ],
        ;

        my $origin = Point3D->new( x => 0, y => 0, z => 0 );

        # or...
        my $origin = Point3D[ 0, 0, 0 ];

DESCRIPTION

       MooX::Struct allows you to create cheap struct-like classes for your data using Moo.

       While similar in spirit to MooseX::Struct and Class::Struct, MooX::Struct has a somewhat
       different usage pattern. Rather than providing you with a "struct" keyword which can be
       used to define structs, you define all the structs as part of the "use" statement. This
       means they happen at compile time.

       A struct is just an "anonymous" Moo class. MooX::Struct creates this class for you, and
       installs a lexical alias for it in your namespace. Thus your module can create a "Point3D"
       struct, and some other module can too, and they won't interfere with each other. All
       struct classes inherit from MooX::Struct.

       Arguments for MooX::Struct are key-value pairs, where keys are the struct names, and
       values are arrayrefs.

        use MooX::Struct
           Person   => [qw/ name address /],
           Company  => [qw/ name address registration_number /];

       The elements in the array are the attributes for the struct (which will be created as
       read-only attributes), however certain array elements are treated specially.

       •   As per the example in the "SYNOPSIS", "-extends" introduces a list of parent classes
           for the struct. If not specified, then classes inherit from MooX::Struct itself.

           Structs can inherit from other structs, or from normal classes. If inheriting from
           another struct, then you must define both in the same "use" statement.  Inheriting
           from a non-struct class is discouraged.

            # Not like this.
            use MooX::Struct Point   => [ 'x', 'y' ];
            use MooX::Struct Point3D => [ -extends => ['Point'], 'z' ];

            # Like this.
            use MooX::Struct
               Point   => [ 'x', 'y' ],
               Point3D => [ -extends => ['Point'], 'z' ],
            ;

       •   Similarly "-with" consumes a list of roles.

       •   If an attribute name is followed by a coderef, this is installed as a method instead.

            use MooX::Struct
               Person => [
                  qw( name age sex ),
                  greet => sub {
                     my $self = shift;
                     CORE::say "Hello ", $self->name;
                  },
               ];

           But if you're defining methods for your structs, then you've possibly missed the point
           of them.

       •   If an attribute name is followed by an arrayref, these are used to set the options for
           the attribute. For example:

            use MooX::Struct
               Person  => [ name => [ is => 'ro', required => 1 ] ];

           Using the "init_arg" option would probably break stuff. Don't do that.

       •   Attribute names may be "decorated" with prefix and postfix "sigils". The prefix sigils
           of "@" and "%" specify that the attribute isa arrayref or hashref respectively.
           (Blessed arrayrefs and hashrefs are accepted; as are objects which overload "@{}" and
           "%{}".) The prefix sigil "$" specifies that the attribute value must not be an
           unblessed arrayref or hashref.  The prefix sigil "+" indicates the attribute is a
           number, and provides a default value of 0, unless the attribute is required. The
           postfix sigil "!" specifies that the attribute is required.

            use MooX::Struct
               Person  => [qw( $name! @children )];

            Person->new();         # dies, name is required
            Person->new(           # dies, children should be arrayref
               name     => 'Bob',
               children => 2,
            );

       Prior to the key-value list, some additional flags can be given. These begin with hyphens.
       The flag "-rw" indicates that attributes should be read-write rather than read-only.

        use MooX::Struct -rw,
           Person => [
              qw( name age sex ),
              greet => sub {
                 my $self = shift;
                 CORE::say "Hello ", $self->name;
              },
           ];

       The "-retain" flag can be used to indicate that MooX::Struct should not use
       namespace::clean to enforce lexicalness on your struct class aliases.

       Flags "-trace" and "-deparse" may be of use debugging.

   Instantiating Structs
       There are two supported methods of instatiating structs. You can use a traditional class-
       like constructor with named parameters:

        my $point = Point->new( x => 1, y => 2 );

       Or you can use the abbreviated syntax with positional parameters:

        my $point = Point[ 1, 2 ];

       If you know about Moo and peek around in the source code for this module, then I'm sure
       you can figure out additional ways to instantiate them, but the above are the only
       supported two.

       When inheritance or roles have been used, it might not always be clear what order the
       positional parameters come in (though see the documentation for the "FIELDS" below), so
       the traditional class-like style may be preferred.

   Methods
       Structs are objects and thus have methods. You can define your own methods as described
       above. MooX::Struct's built-in methods will always obey the convention of being in ALL
       CAPS (except in the case of "_data_printer").  By using lower-case letters to name your
       own methods, you can avoid naming collisions.

       The following methods are currently defined. Additionally all the standard Perl ("isa",
       "can", etc) and Moo ("new", "does", etc) methods are available.

       "OBJECT_ID"
           Returns a unique identifier for the object.

       "FIELDS"
           Returns a list of fields associated with the object. For the "Point3D" struct in the
           SYNPOSIS, this would be 'x', 'y', 'z'.

           The order the fields are returned in is equal to the order they must be supplied for
           the positional constructor.

           Attributes inherited from roles, or from non-struct base classes are not included in
           "FIELDS", and thus cannot be used in the positional constructor.

       "TYPE"
           Returns the type name of the struct, e.g. 'Point3D'.

       "TO_HASH"
           Returns a reference to an unblessed hash where the object's fields are the keys and
           the object's values are the hash values.

       "TO_ARRAY"
           Returns a reference to an unblessed array where the object's values are the array
           items, in the same order as listed by "FIELDS".

       "TO_STRING"
           Joins "TO_ARRAY" with whitespace. This is not necessarily a brilliant stringification,
           but easy enough to overload:

            use MooX::Struct
               Point => [
                  qw( x y ),
                  TO_STRING => sub {
                     sprintf "(%d, %d)"), $_[0]->x, $_[0]->y;
                  },
               ]
            ;

       "CLONE"
           Creates a shallow clone of the object.

       "EXTEND"
           An exverimental feature.

           Extend a class or object with additional attributes, methods, etc. This method takes
           almost all the same arguments as "use MooX::Struct", albeit with some slight
           differences.

            use MooX::Struct Point => [qw/ +x +y /];
            my $point = Point[2, 3];
            $point->EXTEND(-rw, q/+z/);  # extend an object
            $point->can('z');   # true

            my $new_class = Point->EXTEND('+z');  # extend a class
            my $point_3d  = $new_class->new( x => 1, y => 2, z => 3 );
            $point_3d->TYPE;  # Point !

            my $point_4d = $new_class->EXTEND(\"Point4D", '+t');
            $point_4d->TYPE;  # Point4D

            my $origin = Point[]->EXTEND(-with => [qw/ Math::Role::Origin /]);

           This feature has been included mostly because it's easy to implement on top of the
           existing code for processing "use MooX::Struct". Some subsets of this functionality
           are sane, such as the ability to add traits to an object.  Others (like the ability to
           add a new uninitialized, read-only attribute to an existing object) are less sensible.

       "BUILDARGS"
           Moo internal fu.

       "_data_printer"
           Automatic pretty printing with Data::Printer.

            use Data::Printer;
            use MooX::Struct Point => [qw/ +x +y /];
            my $origin = Point[];
            p $origin;

       With the exception of "FIELDS" and "TYPE", any of these can be overridden using the
       standard way of specifying methods for structs.

   Overloading
       MooX::Struct overloads stringification and array dereferencing. Objects always evaluate to
       true in a boolean context. (Even if they stringify to the empty string.)

CAVEATS

       Because you only get an alias for the struct class, you need to be careful with some
       idioms:

          my $point = Point3D->new(x => 1, y => 2, z => 3);
          $point->isa("Point3D");   # false!
          $point->isa( Point3D );   # true

          my %args  = (...);
          my $class = exists $args{z} ? "Point3D" : "Point";  # wrong!
          $class->new(%args);

          my $class = exists $args{z} ?  Point3D  :  Point ;  # right
          $class->new(%args);

BUGS

       Please report any bugs to <http://rt.cpan.org/Dist/Display.html?Queue=MooX-Struct>.

SEE ALSO

       Moo, MooX::Struct::Util, MooseX::Struct, Class::Struct.

AUTHOR

       Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE

       This software is copyright (c) 2012-2013 by Toby Inkster.

       This is free software; you can redistribute it and/or modify it under the same terms as
       the Perl 5 programming language system itself.

DISCLAIMER OF WARRANTIES

       THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
       WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR
       PURPOSE.