Class::Prototyped - Fast prototype-based OO programming in Perl

NAME

Class::Prototyped - Fast prototype-based OO programming in Perl

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SYNOPSIS

    use strict;
    use Class::Prototyped ':EZACCESS';
    $, = ' '; $\ = "\n";
    my $p = Class::Prototyped->new(
      field1 => 123,
      sub1   => sub { print "this is sub1 in p" },
      sub2   => sub { print "this is sub2 in p" }
    );
    $p->sub1;
    print $p->field1;
    $p->field1('something new');
    print $p->field1;
    my $p2 = Class::Prototyped::new(
      'parent*' => $p,
      field2    => 234,
      sub2      => sub { print "this is sub2 in p2" }
    );
    $p2->sub1;
    $p2->sub2;
    print ref($p2), $p2->field1, $p2->field2;
    $p2->field1('and now for something different');
    print ref($p2), $p2->field1;
    $p2->addSlots( sub1 => sub { print "this is sub1 in p2" } );
    $p2->sub1;
    print ref($p2), "has slots", $p2->reflect->slotNames;
    $p2->reflect->include( 'xx.pl' ); # includes xx.pl in $p2's package
    print ref($p2), "has slots", $p2->reflect->slotNames;
    $p2->aa();    # calls aa from included file xx.pl
    $p2->deleteSlots('sub1');
    $p2->sub1;

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DESCRIPTION

This package provides for efficient and simple prototype-based programming in Perl. You can provide different subroutines for each object, and also have objects inherit their behavior and state from another object.

The structure of an object is inspected and modified through mirrors, which are created by calling reflect on an object or class that inherits from Class::Prototyped.

Installation instructions

This module requires Module::Build 0.24 to use the automated installation procedures. With Module::Build installed:

  Build.PL
  perl build test
  perl build install

It can be installed under ActivePerl for Win32 by downloading the PPM from CPAN (the file has the extension .ppm.zip). To install, download the .ppm.zip file, uncompress it, and execute:

  ppm install Class-Prototyped.ppd

The module can also be installed manually by copying lib/Class/Prototyped.pm to perl/site/lib/Class/Prototyped.pm (along with Graph.pm if you want it).

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WHEN TO USE THIS MODULE

When I reach for Class::Prototyped, it's generally because I really need it. When the cleanest way of solving a problem is for the code that uses a module to subclass from it, that is generally a sign that Class::Prototyped would be of use. If you find yourself avoiding the problem by passing anonymous subroutines as parameters to the new method, that's another good sign that you should be using prototype based programming. If you find yourself storing anonymous subroutines in databases, configuration files, or text files, and then writing infrastructure to handle calling those anonymous subroutines, that's yet another sign. When you expect the people using your module to want to change the behavior, override subroutines, and so forth, that's a sign.

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CONCEPTS

Slots

Class::Prototyped borrows very strongly from the language Self (see http://www.sun.com/research/self for more information). The core concept in Self is the concept of a slot. Think of slots as being entries in a hash, except that instead of just pointing to data, they can point to objects, code, or parent objects.

So what happens when you send a message to an object (that is to say, you make a method call on the object)? First, Perl looks for that slot in the object. If it can't find that slot in the object, it searches for that slot in one of the object's parents (which we'll come back to later). Once it finds the slot, if the slot is a block of code, it evaluates the code and returns the return value. If the slot references data, it returns that data. If you assign to a data slot (through a method call), it modifies the data.

Distinguishing data slots and method slots is easy - the latter are references to code blocks, the former are not. Distinguishing parent slots is not so easy, so instead a simple naming convention is used. If the name of the slot ends in an asterisk, the slot is a parent slot. If you have programmed in Self, this naming convention will feel very familiar.

Reflecting

In Self, to examine the structure of an object, you use a mirror. Just like using his shield as a mirror enabled Perseus to slay Medusa, holding up a mirror enables us to look upon an object's structure without name space collisions.

Once you have a mirror, you can add and delete slots like so:

    my $cp = Class::Prototyped->new();
    my $mirror = $cp->reflect();
    $mirror->addSlots(
      field1 => 'foo',
      sub1   => sub {
        print "this is sub1 printing field1: '".$_[0]->field1."'\n";
      },
    );
    $mirror->deleteSlot('sub1');

In addition, there is a more verbose syntax for addSlots where the slot name is replaced by an anonymous array - this is most commonly used to control the slot attributes.

    $cp->reflect->addSlot(
      [qw(field1 FIELD)] => 'foo',
      [qw(sub1 METHOD)]  => sub { print "hi there.\n"; },
    );

Because the mirror methods super, addSlot(s), deleteSlot(s), and getSlot(s) are called frequently on objects, there is an import keyword :EZACCESS that adds methods to the object space that call the appropriate reflected variants.

Slot Attributes

Slot attributes allow the user to specify additional information and behavior relating to a specific slot in an extensible manner. For instance, one might want to mark a specific field slot as constant or to attach a description to a given slot.

Slot attributes are divided up in two ways. The first is by the type of slot - FIELD, METHOD, or PARENT. Some slot attributes apply to all three, some to just two, and some to only one. The second division is on the type of slot attribute:

implementor
These are responsible for implementing the behavior of a slot. An example is a FIELD slot with the attribute constant. A slot is only allowed one implementor. All slot types have a default implementor. For FIELD slots, it is a read-write scalar. For METHOD slots, it is the passed anonymous subroutine. For PARENT slots, implementor and filter slot attributes don't really make sense.

filter
These filter access to the implementor. The quintessential example is the profile attribute. When set, this increments a counter in $Class::Prototyped::Mirror::PROFILE::counts every time the underlying FIELD or METHOD is accessed. Filter attributes can be stacked, so each attribute is assigned a rank with lower values being closer to the implementor and higher values being closer to the caller.

advisory
These slot attributes serve one of two purposes. They can be used to store information about the slot (i.e. description attributes), and they can be used to pass information to the addSlots method (i.e. the promote attribute, which can be used to promote a new PARENT slot ahead of all the existing PARENT slots).

There is currently no formal interface for creating your own attributes - if you feel the need for new attributes, please contact the maintainer first to see if it might make sense to add the new attribute to Class::Prototyped. If not, the contact might provide enough impetus to define a formal interface. The attributes are currently defined in $Class::Prototyped::Mirror::attributes.

Finally, see the defaultAttributes method for information about setting default attributes. This can be used, for instance, to turn on profiling everywhere.

Classes vs. Objects

In Self, everything is an object and there are no classes at all. Perl, for better or worse, has a class system based on packages. We decided that it would be better not to throw out the conventional way of structuring inheritance hierarchies, so in Class::Prototyped, classes are first-class objects.

However, objects are not first-class classes. To understand this dichotomy, we need to understand that there is a difference between the way ``classes'' and the way ``objects'' are expected to behave. The central difference is that ``classes'' are expected to persist whether or not that are any references to them. If you create a class, the class exists whether or not it appears in anyone's @ISA and whether or not there are any objects in it. Once a class is created, it persists until the program terminates.

Objects, on the other hand, should follow the normal behaviors of reference-counted destruction - once the number of references to them drops to zero, they should miraculously disappear - the memory they used needs to be returned to Perl, their DESTROY methods need to be called, and so forth.

Since we don't require this behavior of classes, it's easy to have a way to get from a package name to an object - we simply stash the object that implements the class in $Class::Prototyped::Mirror::objects{$package}. But we can't do this for objects, because if we do the object will persist forever because that reference will always exist.

Weak references would solve this problem, but weak references are still considered alpha and unsupported ($WeakRef::VERSION = 0.01), and we didn't want to make Class::Prototyped dependent on such a module.

So instead, we differentiate between classes and objects. In a nutshell, if an object has an explicit package name (i.e. something other than the auto-generated one), it is considered to be a class, which means it persists even if the object goes out of scope.

To create such an object, use the newPackage method, like so (the encapsulating block exists solely to demonstrate that classes are not scoped):

    {
      my $object = Class::Prototyped->newPackage('MyClass',
          field => 1,
          double => sub {$_[0]->field*2}
        );
    }
    print MyClass->double,"\n";

Notice that the class persists even though $object goes out of scope. If $object were created with an auto-generated package, that would not be true. Thus, for instance, it would be a very, very, very bad idea to add the package name of an object as a parent to another object - when the first object goes out of scope, the package will disappear, but the second object will still have it in it's @ISA.

Except for the crucial difference that you should never, ever, ever make use of the package name for an object for any purpose other than printing it to the screen, objects and classes are simply different ways of inspecting the same entity.

To go from an object to a package, you can do one of the following:

    $package = ref($object);
    $package = $object->reflect->package;

The two are equivalent, although the first is much faster. Just remember, if $object is in an auto-generated package, don't do anything with that $package but print it.

To go from a package to an object, you do this:

    $object = $package->reflect->object;

Note that $package is simple the name of the package - the following code works perfectly:

    $object = MyClass->reflect->object;

But keep in mind that $package has to be a class, not an auto-generated package name for an object.

Class Manipulation

This lets us have tons of fun manipulating classes at run time. For instance, if you wanted to add, at run-time, a new method to the MyClass class? Assuming that the MyClass inherits from Class::Prototyped or that you have specified :REFLECT on the use Class::Prototyped call, you simply write:

    MyClass->reflect->addSlot(myMethod => sub {print "Hi there\n"});

If you want to access a class that doesn't inherit from Class::Prototyped, and you want to avoid specifying :REFLECT (which adds reflect to the UNIVERSAL package), you can make the call like so:

    my $mirror = Class::Prototyped::Mirror->new('MyClass');
    $mirror->addSlot(myMethod => sub {print "Hi there\n"});

Just as you can clone objects, you can clone classes that are derived from Class::Prototyped. This creates a new object that has a copy of all of the slots that were defined in the class. Note that if you simply want to be able to use Data::Dumper on a class, calling MyClass->reflect->object is the preferred approach. Or simply use the dump mirror method.

The code that implements reflection on classes automatically creates slot names for package methods as well as parent slots for the entries in @ISA. This means that you can code classes like you normally do - by doing the inheritance in @ISA and writing package methods.

If you manually add subroutines to a package at run-time and want the slot information updated properly (although this really should be done via the addSlots mechanism, but maybe you're twisted:), you should do something like:

    $package->reflect->_vivified_methods(0);
    $package->reflect->_autovivify_methods;

Parent Slots

Adding parent slots is no different than adding normal slots - the naming scheme takes care of differentiating.

Thus, to add $foo as a parent to $bar, you write:

    $bar->reflect->addSlot('fooParent*' => $foo);

However, keeping with our concept of classes as first class objects, you can also write the following:

    $bar->reflect->addSlot('mixIn*' => 'MyMix::Class');

It will automatically require the module in the namespace of $bar and make the module a parent of the object. This can load a module from disk if needed.

If you're lazy, you can add parents without names like so:

    $bar->reflect->addSlot('*' => $foo);

The slots will be automatically named for the package passed in - in the case of Class::Prototyped objects, the package is of the form PKG0x12345678. In the following example, the parent slot will be named MyMix::Class*.

    $bar->reflect->addSlot('*' => 'MyMix::Class');

Parent slots are added to the inheritance hierarchy in the order that they were added. Thus, in the following code, slots that don't exist in $foo are looked up in $fred (and all of its parent slots) before being looked up in $jill.

    $foo->reflect->addSlots('fred*' => $fred, 'jill*' => $jill);

Note that addSlot and addSlots are identical - the variants exist only because it looks ugly to add a single slot by calling addSlots.

If you need to reorder the parent slots on an object, look at promoteParents. That said, there's a shortcut for prepending a slot to the inheritance hierarchy. Simply define 'promote' as a slot attribute using the extended slot syntax.

Finally, in keeping with our principle that classes are first-class object, the inheritance hierarchy of classes can be modified through addSlots and deleteSlots, just like it can for objects. The following code adds the $foo object as a parent of the MyClass class, prepending it to the inheritance hierarchy:

    MyClass->reflect->addSlots([qw(foo* promote)] => $foo);

Operator Overloading

In Class::Prototyped, you do operator overloading by adding slots with the right name. First, when you do the use on Class::Prototyped, make sure to pass in :OVERLOAD so that the operator overloading support is enabled.

Then simply pass the desired methods in as part of the object creation like so:

    $foo = Class::Prototyped->new(
        value => 3,
        '""'  => sub { my $self = shift; $self->value( $self->value + 1 ) },
    );

This creates an object that increments its field value by one and returns that incremented value whenever it is stringified.

Since there is no way to find out which operators are overloaded, if you add overloading to a class through the use of use overload, that behavior will not show up as slots when reflecting on the class. However, addSlots does work for adding operator overloading to classes. Thus, the following code does what is expected:

    Class::Prototyped->newPackage('MyClass');
    MyClass->reflect->addSlots(
        '""' => sub { my $self = shift; $self->value( $self->value + 1 ) },
    );
    $foo = MyClass->new( value => 2 );
    print $foo, "\n";

Object Class

The special parent slot class* is used to indicate object class. When you create Class::Prototyped objects, the class* slot is not set. If, however, you create objects by calling new on a class that inherits from Class::Prototyped, the slot class* points to the package name.

The value of this slot can be returned quite easily like so:

    $foo->reflect->class;

Class is set when new is called on a package or object that has a named package.

Calling Inherited Methods

Methods (and fields) inherited from prototypes or classes are not generally available using the usual Perl $self->SUPER::something() mechanism.

The reason for this is that SUPER::something is hardcoded to the package in which the subroutine (anonymous or otherwise) was defined. For the vast majority of programs, this will be main::, and thus SUPER:: will look in @main::ISA (not a very useful place to look).

To get around this, a very clever wrapper can be automatically placed around your subroutine that will automatically stash away the package to which the subroutine is attached. From within the subroutine, you can use the super mirror method to make an inherited call. However, because we'd rather not write code that attempts to guess as to whether or not the subroutine uses the super construct, you have to tell addSlots that the subroutine needs to have this wrapper placed around it. To do this, simply use the extended addSlots syntax (see the method description for more information) and pass in the slot attribute 'superable'. The following examples use the minimalist form of the extended syntax.

For instance, the following code will work:

    use Class::Prototyped;
    my $p1 = Class::Prototyped->new(
        method => sub { print "this is method in p1\n" },
    );
    my $p2 = Class::Prototyped->new(
        '*'                     => $p1,
        [qw(method superable)]' => sub {
            print "this is method in p2 calling method in p1: ";
            $_[0]->reflect->super('method');
        },
    );

To make things easier, if you specify :EZACCESS during the import, super can be called directly on an object rather than through its mirror.

The other thing of which you need to be aware is copying methods from one object to another. The proper way to do this is like so:

    $foo->reflect->addSlot($bar->reflect->getSlot('method'));

When the getSlot method is called in an array context, it returns both the complete format for the slot identifier and the slot. This ensures that slot attributes are passed along, including the superable attribute.

Finally, to help protect the code, the super method is smart enough to determine whether it was called within a wrapped subroutine. If it wasn't, it croaks indicating that the method should have had the superable attribute set when it was added. If you wish to disable this checking (which will improve the performance of your code, of course, but could result in very hard to trace bugs if you haven't been careful), see the import option :SUPER_FAST.

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PERFORMANCE NOTES

It is important to be aware of where the boundaries of prototyped based programming lie, especially in a language like Perl that is not optimized for it. For instance, it might make sense to implement every field in a database as an object. Those field objects would in turn be attached to a record class. All of those might be implemented using Class::Prototyped. However, it would be very inefficient if every record that got read from the database was stored in a Class::Prototyped based object (unless, of course, you are storing code in the database). In that situation, it is generally good to choke off the prototype-based behavior for the individual record objects. For best performance, it is important to confine Class::Prototyped to those portions of the code where behavior is mutable from outside of the module. See the documentation for the new method of Class::Prototyped for more information about choking off Class::Prototyped behavior.

There are a number of performance hits when using Class::Prototyped, relative to using more traditional OO code. It is important to note that these generally lie in the instantiation and creation of classes and objects and not in the actual use of them. The scripts in the perf directory were designed for benchmarking some of this material.

Class Instantiation

The normal way of creating a class is like this:

    package Pack_123;
    sub a {"hi";}
    sub b {"hi";}
    sub c {"hi";}
    sub d {"hi";}
    sub e {"hi";}

The most efficient way of doing that using ``proper'' Class::Prototyped methodology looks like this:

    Class::Prototyped->newPackage("Pack_123");
    push(@P_123::slots, a => sub {"hi";});
    push(@P_123::slots, b => sub {"hi";});
    push(@P_123::slots, c => sub {"hi";});
    push(@P_123::slots, d => sub {"hi";});
    push(@P_123::slots, e => sub {"hi";});
    Pack_123->reflect->addSlots(@P_123::slots);

This approach ensures that the new package gets the proper default attributes and that the slots are created through addSlots, thus ensuring that default attributes are properly implemented. It avoids multiple calls to ->reflect->addSlot, though, which improves performance. The idea behind pushing the slots onto an array is that it enables one to intersperse code with POD, since POD is not permitted inside of a single Perl statement.

On a Pent 4 1.8GHz machine, the normal code runs in 120 usec, whereas the Class::Prototyped code runs in around 640 usec, or over 5 times slower. A straight call to addSlots with all five methods runs in around 510 usec. Code that creates the package and the mirror without adding slots runs in around 135 usec, so we're looking at an overhead of less than 100 usec per slot. In a situation where the ``compile'' time dominates the ``execution'' time (I'm using those terms loosely as much of what happens in Class::Prototyped is technically execution time, but it is activity that traditionally would happen at compile time), Class::Prototyped might prove to be too much overhead. On the otherhand, you may find that demand loading can cut much of that overhead and can be implemented less painfully than might otherwise be thought.

Object Instantiation

There is no need to even compare here. Blessing a hash into a class takes less than 2 usec. Creating a new Class::Prototyped object takes at least 60 or 70 times longer. The trick is to avoid creating unnecessary Class::Prototyped objects. If you know that all 10,000 database records are going to inherit all of their behavior from the parent class, there is no point in creating 10,000 packages and all the attendant overhead. The new method for Class::Prototyped demonstrates how to ensure that those state objects are created as normal Perl objects.

Method Calls

The good news is that method calls are just as fast as normal Perl method calls, inherited or not. This is because the existing Perl OO machinery has been hijacked in Class::Prototyped. The exception to this is if filter slot attributes have been used, including wantarray, superable, and profile. In that situation, the added overhead is that for a normal Perl subroutine call (which is faster than a method call because it is a static binding)

Instance Variable Access

The hash interface is not particularly fast, and neither is it good programming practice. Using the method interface to access fields is just as fast, however, as using normal getter/setter methods.

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IMPORT OPTIONS

:OVERLOAD
This configures the support in Class::Prototyped for using operator overloading.

:REFLECT
This defines UNIVERSAL::reflect to return a mirror for any class. With a mirror, you can manipulate the class, adding or deleting methods, changing its inheritance hierarchy, etc.

:EZACCESS
This adds the methods addSlot, addSlots, deleteSlot, deleteSlots, getSlot, getSlots, and super to Class::Prototyped.

This lets you write:

  $foo->addSlot(myMethod => sub {print "Hi there\n"});

instead of having to write:

  $foo->reflect->addSlot(myMethod => sub {print "Hi there\n"});

The other methods in Class::Prototyped::Mirror should be accessed through a mirror (otherwise you'll end up with way too much name space pollution for your objects:).

Note that it is bad form for published modules to use :EZACCESS as you are polluting everyone else's namespace as well. If you really want :EZACCESS for code you plan to publish, contact the maintainer and we'll see what we can about creating a variant of :EZACCESS that adds the shortcut methods to a single class. Note that using :EZACCESS to do $obj->addSlot() is actually slower than doing $obj->reflect->addSlot().

:SUPER_FAST
Switches over to the fast version of super that doesn't check to see whether slots that use inherited calls were defined as superable.

:NEW_MAIN
Creates a new function in main:: that creates new Class::Prototyped objects. Thus, you can write code like: 
  use Class::Prototyped qw(:NEW_MAIN :EZACCESS);
  my $foo = new(say_hi => sub {print "Hi!\n";});
  $foo->say_hi;

:TIED_INTERFACE
This is no longer supported. Sorry for the very short notice - if you have a specific need, please let me know and I will discuss your needs with you and determine whether they can be addressed in a manner that doesn't require you to rewrite your code, but still allows others to make use of less global control over the tied interfaces used. See Class::Prototyped::Mirror::tiedInterfacePackage for the preferred way of doing this.

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Class::Prototyped Methods

new() - Construct a new Class::Prototyped object.

A new object is created. If this is called on a class that inherits from Class::Prototyped, and class* is not being passed as a slot in the argument list, the slot class* will be the first element in the inheritance list.

The passed arguments are handed off to addSlots.

For instance, the following will define a new Class::Prototyped object with two method slots and one field slot:

    my $foo = Class::Prototyped->new(
        field1 => 123,
        sub1   => sub { print "this is sub1 in foo" },
        sub2   => sub { print "this is sub2 in foo" },
    );

The following will create a new MyClass object with one field slot and with the parent object $bar at the beginning of the inheritance hierarchy (just before class*, which points to MyClass):

    my $foo = MyClass->new(
        field1  => 123,
        [qw(bar* promote)] => $bar,
    );

If you want to create normal Perl objects as child objects of a Class::Prototyped class in order to improve performance, implement your own standard Perl new method:

    Class::Prototyped->newPackage('MyClass');
    MyClass->reflect->addSlot(
        new => sub {
            my $class = shift;
            my $self = {};
            bless $self, $class;
            return $self;
        }
    );

It is still safe to use $obj->reflect->super() in code that runs on such an object. All other reflection will automatically return the same results as inspecting the class to which the object belongs.

newPackage() - Construct a new Class::Prototyped object in a specific package.

Just like new, but instead of creating the new object with an arbitrary package name (actually, not entirely arbitrary - it's generally based on the hash memory address), the first argument is used as the name of the package.

If the package name is already in use, this method will croak.

clone() - Duplicate me

Duplicates an existing object or class. and allows you to add or override slots. The slot definition is the same as in new().

  my $p2 = $p1->clone(
      sub1 => sub { print "this is sub1 in p2" },
  );

It calls new on the object to create the new object, so if new has been overriden, the overriden new will be called.

reflect() - Return a mirror for the object or class

The structure of an object is modified by using a mirror. This is the equivalent of calling:

  Class::Prototyped::Mirror->new($foo);

destroy() - The destroy method for an object

You should never need to call this method. However, you may want to override it. Because we had to directly specify DESTROY for every object in order to allow safe destruction during global destruction time when objects may have already destroyed packages in their @ISA, we had to hook DESTROY for every object. To allow the destroy behavior to be overridden, users should specify a destroy method for their objects (by adding the slot), which will automatically be called by the Class::Prototyped::DESTROY method after the @ISA has been cleaned up.

This method should be defined to allow inherited method calls (i.e. should use ``[qw(destroy superable)]'' to define the method) and should call $self->reflect->super('destroy'); at some point in the code.

Here is a quick overview of the default destruction behavior for objects:

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Class::Prototyped::Mirror Methods

These are the methods you can call on the mirror returned from a reflect call. If you specify :EZACCESS in the use Class::Prototyped line, addSlot, addSlots, deleteSlot, deleteSlots, getSlot, getSlots, and super will be callable on Class::Prototyped objects as well.

new() - Creates a new Class::Prototyped::Mirror object

Normally called via the reflect method, this can be called directly to avoid using the :REFLECT import option for reflecting on non Class::Prototyped based classes.

autoloadCall()

If you add an AUTOLOAD slot to an object, you will need to get the name of the subroutine being called. autoloadCall() returns the name of the subroutine, with the package name stripped off.

package() - Returns the name of the package for the object

object() - Returns the object itself

class() - Returns the class* slot for the underlying object

dump() - Returns a Data::Dumper string representing the object

addSlot() - An alias for addSlots

addSlots() - Add or replace slot definitions

Allows you to add or replace slot definitions in the receiver.

    $p->reflect->addSlots(
        fred        => 'this is fred',
        doSomething => sub { print 'doing something with ' . $_[1] },
    );
    $p->doSomething( $p->fred );

In addition to the simple form, there is an extended syntax for specifying the slot. In place of the slotname, pass an array reference composed like so:

addSlots( [$slotName, $slotType, %slotAttributes] => $slotValue );

$slotName is simply the name of the slot, including the trailing * if it is a parent slot. $slotType should be 'FIELD', 'METHOD', or 'PARENT'. %slotAttributes should be a list of attribute/value pairs. It is common to use qw() to reduce the amount of typing:

    $p->reflect->addSlot(
        [qw(bar FIELD)] => "this is a field",
    );
    $p->reflect->addSlot(
        [qw(bar FIELD constant 1)] => "this is a constant field",
    );
    $p->reflect->addSlot(
        [qw(foo METHOD)] => sub { print "normal method.\n"; },
    );
    $p->reflect->addSlot(
        [qw(foo METHOD superable 1)] => sub { print "superable method.\n"; },
    );
    $p->reflect->addSlot(
        [qw(parent* PARENT)] => $parent,
    );
    $p->reflect->addSlot(
        [qw(parent2* PARENT promote 1)] => $parent2,
    );

To make using the extended syntax a bit less cumbersome, however, the following shortcuts are allowed:

Using both of the above contractions, the following are valid short forms for the extended syntax:

    $p->reflect->addSlot(
        [qw(bar constant)] => "this is a constant field",
    );
    $p->reflect->addSlot(
        [qw(foo superable)] => sub { print "superable method.\n"; },
    );
    $p->reflect->addSlot(
        [qw(parent2* promote)] => $parent2,
    );

The currently defined slot attributes are as follows:

FIELD Slots
constant (implementor)
When true, this defines the field slot as constant, disabling the ability to modify it using the $object->field($newValue) syntax. The value may still be modified using the hash syntax (i.e. $object->{field} = $newValue). This is mostly useful if you have an object method call that takes parameters, but you wish to replace it on a given object with a hard-coded value by using a field (which makes inspecting the value of the slot through Data::Dumper much easier than if you use a METHOD slot to return the constant, since code objects are opaque).

autoload (filter, rank 50)
The passed value for the FIELD slot should be a subroutine that returns the desired value. Upon the first access, the subroutine will be called, the return value hard-coded into the object by adding the slot (including all otherwise specified attributes), and the value then returned. Useful for implementing constant slots that are costly to initialize, especially those that return lists of Class::Prototyped objects!

profile (filter, rank 80)
If profile is set to 1, increments $Class::Prototyped::Mirror::PROFILE::counts->{$package}->{$slotName} everytime the slot is accessed. If profile is set to 2, increments $Class::Prototyped::Mirror::PROFILE::counts->{$package}->{$slotName}->{$caller} everytime the slot is accessed, where $caller is "$file ($line)".

wantarray (filter, rank 90)
If the field specifies a reference to an array and the call is in list context, dereferences the array and returns a list of values.

description (advisory)
Can be used to specify a description. No real support for this yet beyond that!

METHOD Slots
superable (filter, rank 10)
When true, this enables the $self->reflect->super( . . . ) calls for this method slot.

profile (filter, rank 90)
See FIELD slots for explanation.

overload (advisory)
Set automatically for methods that implement operator overloading.

description (advisory)
See FIELD slots for explanation.

PARENT Slots
promote (advisory)
When true, this parent slot is promoted ahead of any other parent slots on the object. This attribute is ephemeral - it is not returned by calls to getSlot.

description (advisory)
See FIELD slots for explanation.

deleteSlot() - An alias for deleteSlots

deleteSlots() - Delete one or more of the receiver's slots by name

This will let you delete existing slots in the receiver. If those slots were defined in the receiver's inheritance hierarchy, those inherited definitions will now be available.

    my $p1 = Class::Prototyped->new(
        field1 => 123,
        sub1   => sub { print "this is sub1 in p1" },
        sub2   => sub { print "this is sub2 in p1" }
    );
    my $p2 = Class::Prototyped->new(
        'parent*' => $p1,
        sub1      => sub { print "this is sub1 in p2" },
    );
    $p2->sub1;    # calls $p2.sub1
    $p2->reflect->deleteSlots('sub1');
    $p2->sub1;    # calls $p1.sub1
    $p2->reflect->deleteSlots('sub1');
    $p2->sub1;    # still calls $p1.sub1

super() - Call a method defined in a parent

The call to a method defined on a parent that is obscured by the current one looks like so:

    $self->reflect->super('method_name', @params);

slotNames() - Returns a list of all the slot names

This is passed an optional type parameter. If specified, it should be one of 'FIELD', 'METHOD', or 'PARENT'. For instance, the following will print out a list of all slots of an object:

  print join(', ', $obj->reflect->slotNames)."\n";

The following would print out a list of all field slots:

  print join(', ', $obj->reflect->slotNames('FIELD')."\n";

The parent slot names are returned in the same order for which inheritance is done.

slotType() - Given a slot name, determines the type

This returns 'FIELD', 'METHOD', or 'PARENT'. It croaks if the slot is not defined for that object.

parents() - Returns a list of all parents

Returns a list of all parent object (or package names) for this object.

allParents() - Returns a list of all parents in the hierarchy

Returns a list of all parent objects (or package names) in the object's hierarchy.

withAllParents() - Same as above, but includes self in the list

allSlotNames() - Returns a list of all slot names defined for the entire inheritance hierarchy

Note that this will return duplicate slot names if inherited slots are obscured.

getSlot() - Returns the requested slot

When called in scalar context, this returns the thing in the slot. When called in list context, it returns both the complete form of the extended syntax for specifying a slot name and the thing in the slot. There is an optional parameter that can be used to modify the format of the return value in list context. The allowable values are:

The latter two options are quite useful when used in conjunction with the getSlots method.

getSlots() - Returns a list of all the slots

This returns a list of extended syntax slot specifiers and their values ready for sending to addSlots. It takes first the optional parameter passed to slotNames which specifies the type of slot ('FIELD', 'METHOD', 'PARENT', or undef) and then the optional parameter passed to getSlot, which specifies the format for the return value. If the latter is 'simple', the returned values can be passed to addSlots, but any non-default slot attributes (i.e. superable or constant) will be lost. If the latter is 'rotated', the returned values are completely inappropriate for passing to addSlots. Both 'simple' and 'rotated' are appropriate for assigning the return values into a hash.

For instance, to add all of the field slots in $bar to $foo:

  $foo->reflect->addSlots($bar->reflect->getSlots('FIELD'));

To get a list of all of the slots in the 'simple' format:

  my %barSlots = $bar->reflect->getSlots(undef, 'simple');

To get a list of all of the superable method slots in the 'rotated' format:

  my %barMethods = $bar->reflect->getSlots('METHOD', 'rotated');
  foreach my $slotName (%barMethods) {
    delete $barMethods{$slotName}
      unless $barMethods{$slotName}->{attribs}->{superable};
  }

promoteParents() - This changes the ordering of the parent slots

This expects a list of parent slot names. There should be no duplicates and all of the parent slot names should be already existing parent slots on the object. These parent slots will be moved forward in the hierarchy in the order that they are passed. Unspecified parent slots will retain their current positions relative to other unspecified parent slots, but as a group they will be moved to the end of the hierarchy.

tiedInterfacePackage() - This specifies the tied interface package

This allows you to specify the sort of tied interface you wish to offer when code accesses the object as a hash reference. If no parameter is passed, this will return the current tied interface package active for the object. If a parameter is passed, it should specify either the package name or an alias. The currently known aliases are:

default
This specifies Class::Prototyped::Tied::Default as the tie class. The default behavior is to allow access to existing fields, but attempts to create fields, access methods, or delete slots will croak. This is the tie class used by Class::Prototyped (unless you do something very naughty and call Class::Prototyped->reflect->tiedInterfacePackage($not_default)), and as such is the fallback behavior for classes and objects if they don't get a different value from their inheritance.

autovivify
This specifies Class::Prototyped::Tied::AutoVivify as the tie class. The behavior of this package allows access to existing fields, will automatically create field slots if they don't exist, and will allow deletion of field slots. Attempts to access or delete method or parent slots will croak.

Calls to new and clone will use the tied interface in use on the existing object/package. When reflect is called for the first time on a class package, it will use the tied interface of its first parent class (i.e. $ISA[0]). If that package has not yet had reflect called on it, it will check its parent, and so on and so forth. If none of the packages in the primary inheritance fork have been reflected upon, the value for Class::Prototyped will be used, which should be default.

defaultAttributes() - get and set default attributes

This isn't particularly pretty. The general syntax looks something like:

    my $temp = MyClass->reflect->defaultAttributes;
    $temp->{METHOD}->{superable} = 1;
    MyClass->reflect->defaultAttributes($temp);

The return value from defaultAttributes is a hash with the keys 'FIELD', 'METHOD', and 'PARENT'. The values are either undef or hash references consisting of the attributes and their default values. Modify the data structure as desired and pass it back to defaultAttributes to change the default attributes for that object or class. Note that default attributes are not inherited dynamically - the inheritance occurs when a new object is created, but from that point on changes to a parent object are not inherited by the child. Global changes can be effected by modifying the defaultAttributes for Class::Prototyped in a sufficiently early BEGIN block. Note that making global changes like this is not recommended for production modules as it may interfere with other modules that rely upon Class::Prototyped.

wrap()

unwrap()

delegate()

delegate name => slot name can be string, regex, or array of same. slot can be slot name, or object, or 2-element array with slot name or object and method name. You can delegate to a parent.

include() - include a package or external file

You can require an arbitrary file in the namespace of an object or class without adding to the parents using include() :

  $foo->include( 'xx.pl' );

will include whatever is in xx.pl. Likewise for modules:

  $foo->include( 'MyModule' );

will search along your @INC path for MyModule.pm and include it.

You can specify a second parameter that will be the name of a subroutine that you can use in your included code to refer to the object into which the code is being included (as long as you don't change packages in the included code). The subroutine will be removed after the include, so don't call it from any subroutines defined in the included code.

If you have the following in File.pl:

    sub b {'xxx.b'}
    sub c { return thisObject(); }    # DON'T DO THIS!
    thisObject()->reflect->addSlots(
        'parent*' => 'A',
        d         => 'added.d',
        e         => sub {'xxx.e'},
    );

And you include it using:

    $mirror->include('File.pl', 'thisObject');

Then the addSlots will work fine, but if sub c is called, it won't find thisObject().

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AUTHOR

Written by Ned Konz, perl@bike-nomad.com and Toby Ovod-Everett, toby@ovod-everett.org. 5.005_03 porting by chromatic.

Toby Ovod-Everett is currently maintaining the package.

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LICENSE

Copyright 2001-2004 Ned Konz and Toby Ovod-Everett. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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SEE ALSO

the Class::SelfMethods manpage

the Class::Object manpage

the Class::Classless manpage

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 Class::Prototyped - Fast prototype-based OO programming in Perl