NAME

    Spiffy - Spiffy Perl Interface Framework For You

SYNOPSIS

        package Keen;

        use Spiffy -Base;

        field 'mirth';

        const mood => ':-)';

        sub happy {

            if ($self->mood eq ':-(') {

                $self->mirth(-1);

                print "Cheer up!";

            }

            super;

        }

DESCRIPTION

    "Spiffy" is a framework and methodology for doing object oriented (OO)

    programming in Perl. Spiffy combines the best parts of Exporter.pm,

    base.pm, mixin.pm and SUPER.pm into one magic foundation class. It

    attempts to fix all the nits and warts of traditional Perl OO, in a

    clean, straightforward and (perhaps someday) standard way.

    Spiffy borrows ideas from other OO languages like Python, Ruby, Java and

    Perl 6. It also adds a few tricks of its own.

    If you take a look on CPAN, there are a ton of OO related modules. When

    starting a new project, you need to pick the set of modules that makes

    most sense, and then you need to use those modules in each of your

    classes. Spiffy, on the other hand, has everything you'll probably need

    in one module, and you only need to use it once in one of your classes.

    If you make Spiffy.pm the base class of the basest class in your

    project, Spiffy will automatically pass all of its magic to all of your

    subclasses. You may eventually forget that you're even using it!

    The most striking difference between Spiffy and other Perl object

    oriented base classes, is that it has the ability to export things. If

    you create a subclass of Spiffy, all the things that Spiffy exports will

    automatically be exported by your subclass, in addition to any more

    things that you want to export. And if someone creates a subclass of

    your subclass, all of those things will be exported automatically, and

    so on. Think of it as "Inherited Exportation", and it uses the familiar

    Exporter.pm specification syntax.

    To use Spiffy or any subclass of Spiffy as a base class of your class,

    you specify the "-base" argument to the "use" command.

        use MySpiffyBaseModule -base;

    You can also use the traditional "use base 'MySpiffyBaseModule';" syntax

    and everything will work exactly the same. The only caveat is that

    Spiffy.pm must already be loaded. That's because Spiffy rewires base.pm

    on the fly to do all the Spiffy magics.

    Spiffy has support for Ruby-like mixins with Perl6-like roles. Just like

    "base" you can use either of the following invocations:

        use mixin 'MySpiffyBaseModule';

        use MySpiffyBaseModule -mixin;

    The second version will only work if the class being mixed in is a

    subclass of Spiffy. The first version will work in all cases, as long as

    Spiffy has already been loaded.

    To limit the methods that get mixed in, use roles. (Hint: they work just

    like an Exporter list):

        use MySpiffyBaseModule -mixin => qw(:basics x y !foo);

    In object oriented Perl almost every subroutine is a method. Each method

    gets the object passed to it as its first argument. That means

    practically every subroutine starts with the line:

        my $self = shift;

    Spiffy provides a simple, optional filter mechanism to insert that line

    for you, resulting in cleaner code. If you figure an average method has

    10 lines of code, that's 10% of your code! To turn this option on, you

    just use the "- Base" option instead of the "-base" option, or add the

    "-selfless" option. If source filtering makes you queazy, don't use the

    feature. I personally find it addictive in my quest for writing squeaky

    clean, maintainable code.

    A useful feature of Spiffy is that it exports two functions: "field" and

    "const" that can be used to declare the attributes of your class, and

    automatically generate accessor methods for them. The only difference

    between the two functions is that "const" attributes can not be

    modified; thus the accessor is much faster.

    One interesting aspect of OO programming is when a method calls the same

    method from a parent class. This is generally known as calling a super

    method. Perl's facility for doing this is butt ugly:

        sub cleanup {

            my $self = shift;

            $self->scrub;

            $self->SUPER::cleanup(@_);

        }

    Spiffy makes it, er, super easy to call super methods. You just use the

    "super" function. You don't need to pass it any arguments because it

    automatically passes them on for you. Here's the same function with

    Spiffy:

        sub cleanup {

            $self->scrub;

            super;

        }

    Spiffy has a special method for parsing arguments called

    "parse_arguments", that it also uses for parsing its own arguments. You

    declare which arguments are boolean (singletons) and which ones are

    paired, with two special methods called "boolean_arguments" and

    "paired_arguments". Parse arguments pulls out the booleans and pairs and

    returns them in an anonymous hash, followed by a list of the unmatched

    arguments.

    Finally, Spiffy can export a few debugging functions "WWW", "XXX", "YYY"

    and "ZZZ". Each of them produces a YAML dump of its arguments. WWW warns

    the output, XXX dies with the output, YYY prints the output, and ZZZ

    confesses the output. If YAML doesn't suit your needs, you can switch

    all the dumps to Data::Dumper format with the "-dumper" option.

    That's Spiffy!

EXPORTING

    Spiffy implements a completely new idea in Perl. Modules that act both

    as object oriented classes and that also export functions. But it takes

    the concept of Exporter.pm one step further; it walks the entire @ISA

    path of a class and honors the export specifications of each module.

    Since Spiffy calls on the Exporter module to do this, you can use all

    the fancy interface features that Exporter has, including tags and

    negation.

    Spiffy considers all the arguments that don't begin with a dash to

    comprise the export specification.

        package Vehicle;

        use Spiffy -base;

        our $SERIAL_NUMBER = 0;

        our @EXPORT = qw($SERIAL_NUMBER);

        our @EXPORT_BASE = qw(tire horn);

        package Bicycle;

        use Vehicle -base, '!field';

        $self->inflate(tire);

    In this case, "Bicycle->isa('Vehicle')" and also all the things that

    "Vehicle" and "Spiffy" export, will go into "Bicycle", except "field".

    Exporting can be very helpful when you've designed a system with

    hundreds of classes, and you want them all to have access to some

    functions or constants

          or variables. Just export them in your main base class and every subclass

    will get the functions they need.

    You can do almost everything that Exporter does because Spiffy delegates

    the job to Exporter (after adding some Spiffy magic). Spiffy offers a

    @EXPORT_BASE variable which is like @EXPORT, but only for usages that

    use "-base".

MIXINS & ROLES

    If you've done much OO programming in Perl you've probably used Multiple

    Inheritance (MI), and if you've done much MI you've probably run into

    weird problems and headaches. Some languages like Ruby, attempt to

    resolve MI issues using a technique called mixins. Basically, all Ruby

    classes use only Single Inheritance (SI), and then *mixin* functionality

    from other modules if they need to.

    Mixins can be thought of at a simplistic level as *importing* the

    methods of another class into your subclass. But from an implementation

    standpoint that's not the best way to do it. Spiffy does what Ruby does.

    It creates an empty anonymous class, imports everything into that class,

    and then chains the new class into your SI ISA path. In other words, if

    you say:

        package AAA;

        use BBB -base;

        use CCC -mixin;

        use DDD -mixin;

    You end up with a single inheritance chain of classes like this:

        AAA << AAA-DDD << AAA-CCC << BBB;

    "AAA-DDD" and "AAA-CCC" are the actual package names of the generated

    classes. The nice thing about this style is that mixing in CCC doesn't

    clobber any methods in AAA, and DDD doesn't conflict with AAA or CCC

    either. If you mixed in a method in CCC that was also in AAA, you can

    still get to it by using "super".

    When Spiffy mixes in CCC, it pulls in all the methods in CCC that do not

    begin with an underscore. Actually it goes farther than that. If CCC is

    a subclass it will pull in every method that CCC "can" do through

    inheritance. This is very powerful, maybe too powerful.

    To limit what you mixin, Spiffy borrows the concept of Roles from Perl6.

    The term role is used more loosely in Spiffy though. It's much like an

    import list that the Exporter module uses, and you can use groups (tags)

    and negation. If the first element of your list uses negation, Spiffy

    will start with all the methods that your mixin class can do.

        use EEE -mixin => qw(:tools walk !run !:sharp_tools);

    In this example, "walk" and "run" are methods that EEE can do, and

    "tools" and "sharp_tools" are roles of class EEE. How does class EEE

    define these roles? It very simply defines methods called "_role_tools"

    and "_role_sharp_tools" which return lists of more methods. (And

    possibly other roles!) The neat thing here is that since roles are just

    methods, they too can be inherited. Take that Perl6!

FILTERING

    By using the "-Base" flag instead of "-base" you never need to write the

    line:

        my $self = shift;

    This statement is added to every subroutine in your class by using a

    source filter. The magic is simple and fast, so there is litte

    performance penalty for creating clean code on par with Ruby and Python.

        package Example;

        use Spiffy -Base;

        sub crazy {

            $self->nuts;

        }

        sub wacky { }

        sub new() {

            bless [], shift;

        }

    is exactly the same as:

        package Example;

        use Spiffy -base;

        use strict;use warnings;

        sub crazy {my $self = shift;

            $self->nuts;

        }

        sub wacky {my $self = shift; }

        sub new {

            bless [], shift;

        }

        ;1;

    Note that the empty parens after the subroutine "new" keep it from

    having a $self added. Also note that the extra code is added to existing

    lines to ensure that line numbers are not altered.

    "-Base" also turns on the strict and warnings pragmas, and adds that

    annoying '1;' line to your module.

PRIVATE METHODS

    Spiffy now has support for private methods when you use the '-Base'

    filter mechanism. You just declare the subs with the "my" keyword, and

    call them with a '$' in front. Like this:

        package Keen;

        use SomethingSpiffy -Base;

        # normal public method

        sub swell {

            $self->$stinky;

        }

        # private lexical method. uncallable from outside this file.

        my sub stinky {

            ...

        }

SPIFFY DEBUGGING

    The XXX function is very handy for debugging because you can insert it

    almost anywhere, and it will dump your data in nice clean YAML. Take the

    following statement:

        my @stuff = grep { /keen/ } $self->find($a, $b);

    If you have a problem with this statement, you can debug it in any of

    the following ways:

        XXX my @stuff = grep { /keen/ } $self->find($a, $b);

        my @stuff = XXX grep { /keen/ } $self->find($a, $b);

        my @stuff = grep { /keen/ } XXX $self->find($a, $b);

        my @stuff = grep { /keen/ } $self->find(XXX $a, $b);

    XXX is easy to insert and remove. It is also a tradition to mark

    uncertain areas of code with XXX. This will make the debugging dumpers

    easy to spot if you forget to take them out.

    WWW and YYY are nice because they dump their arguments and then return

    the arguments. This way you can insert them into many places and still

    have the code run as before. Use ZZZ when you need to die with both a

    YAML dump and a full stack trace.

    The debugging functions are exported by default if you use the "-base"

    option, but only if you have previously used the "-XXX" option. To

    export all 4 functions use the export tag:

        use SomeSpiffyModule ':XXX';

    To force the debugging functions to use Data::Dumper instead of YAML:

        use SomeSpiffyModule -dumper;

SPIFFY FUNCTIONS

    This section describes the functions the Spiffy exports. The "field",

    "const", "stub" and "super" functions are only exported when you use the

    "-base" or "-Base" options.

    field

        Defines accessor methods for a field of your class:

            package Example;

            use Spiffy -Base;

            field 'foo';

            field bar => [];

            sub lalala {

                $self->foo(42);

                push @{$self->{bar}}, $self->foo;

            }

        The first parameter passed to "field" is the name of the attribute

        being defined. Accessors can be given an optional default value.

        This value will be returned if no value for the field has been set

        in the object.

    const

            const bar => 42;

        The "const" function is similar to <field> except that it is

        immutable. It also does not store data in the object. You probably

        always want to give a "const" a default value, otherwise the

        generated method will be somewhat useless.

    stub

            stub 'cigar';

        The "stub" function generates a method that will die with an

        appropriate message. The idea is that subclasses must implement

        these methods so that the stub methods don't get called.

    super

        If this function is called without any arguments, it will call the

        same method that it is in, higher up in the ISA tree, passing it all

        the same arguments. If it is called with arguments, it will use

        those arguments with $self in the front. In other words, it just

        works like you'd expect.

            sub foo {

                super;             # Same as $self->SUPER::foo(@_);

                super('hello');    # Same as $self->SUPER::foo('hello');

                $self->bar(42);

            }

            sub new() {

                my $self = super;

                $self->init;

                return $self;

            }

        "super" will simply do nothing if there is no super method. Finally,

        "super" does the right thing in AUTOLOAD subroutines.

METHODS

    This section lists all of the methods that any subclass of Spiffy

    automatically inherits.

    mixin

        A method to mixin a class at runtime. Takes the same arguments as

        "use mixin ...". Makes the target class a mixin of the caller.

            $self->mixin('SomeClass');

            $object->mixin('SomeOtherClass' => 'some_method');

    parse_arguments

        This method takes a list of arguments and groups them into pairs. It

        allows for boolean arguments which may or may not have a value

        (defaulting to 1). The method returns a hash reference of all the

        pairs as keys and values in the hash. Any arguments that cannot be

        paired, are returned as a list. Here is an example:

            sub boolean_arguments { qw(-has_spots -is_yummy) }

            sub paired_arguments { qw(-name -size) }

            my ($pairs, @others) = $self->parse_arguments(

                'red', 'white',

                -name => 'Ingy',

                -has_spots =>

                -size => 'large',

                'black',

                -is_yummy => 0,

            );

        After this call, $pairs will contain:

            {

                -name => 'Ingy',

                -has_spots => 1,

                -size => 'large',

                -is_yummy => 0,

            }

        and @others will contain 'red', 'white', and 'black'.

    boolean_arguments

        Returns the list of arguments that are recognized as being boolean.

        Override this method to define your own list.

    paired_arguments

        Returns the list of arguments that are recognized as being paired.

        Override this method to define your own list.

ARGUMENTS

    When you "use" the Spiffy module or a subclass of it, you can pass it a

    list of arguments. These arguments are parsed using the

    "parse_arguments" method described above. The special argument "-base",

    is used to make the current package a subclass of the Spiffy module

    being used.

    Any non-paired parameters act like a normal import list; just like those

    used with the Exporter module.

USING SPIFFY WITH BASE.PM

    The proper way to use a Spiffy module as a base class is with the

    "-base" parameter to the "use" statement. This differs from typical

    modules where you would want to "use base".

        package Something;

        use Spiffy::Module -base;

        use base 'NonSpiffy::Module';

    Now it may be hard to keep track of what's Spiffy and what is not.

    Therefore Spiffy has actually been made to work with base.pm. You can

    say:

        package Something;

        use base 'Spiffy::Module';

        use base 'NonSpiffy::Module';

    "use base" is also very useful when your class is not an actual module

    (a separate file) but just a package in some file that has already been

    loaded. "base" will work whether the class is a module or not, while the

    "-base" syntax cannot work that way, since "use" always tries to load a

    module.

  base.pm Caveats

    To make Spiffy work with base.pm, a dirty trick was played. Spiffy swaps

    "base::import" with its own version. If the base modules are not Spiffy,

    Spiffy calls the original base::import. If the base modules are Spiffy,

    then Spiffy does its own thing.

    There are two caveats.

    Spiffy must be loaded first.

        If Spiffy is not loaded and "use base" is invoked on a Spiffy

        module, Spiffy will die with a useful message telling the author to

        read this documentation. That's because Spiffy needed to do the

        import swap beforehand.

        If you get this error, simply put a statement like this up front in

        your code:

            use Spiffy ();

    No Mixing

        "base.pm" can take multiple arguments. And this works with Spiffy as

        long as all the base classes are Spiffy, or they are all non-Spiffy.

        If they are mixed, Spiffy will die. In this case just use separate

        "use base" statements.

SPIFFY TODO LIST

    Spiffy is a wonderful way to do OO programming in Perl, but it is still

    a work in progress. New things will be added, and things that don't work

    well, might be removed.

AUTHOR

    Ingy döt Net <ingy@cpan.org>

COPYRIGHT AND LICENSE

    Copyright 2004-2014. Ingy döt Net.

    This program is free software; you can redistribute it and/or modify it

    under the same terms as Perl itself.

    See <http://www.perl.com/perl/misc/Artistic.html>