Provided by: libclass-prototyped-perl_1.16-1_all 
NAME
"Class::Prototyped" - Fast prototype-based OO programming in Perl
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;
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).
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.
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. Even easier would be to 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 by calling "Class::Prototyped->new()", the "class*" slot is not set. If, however, you create
objects by calling "new" on a class or object that inherits from "Class::Prototyped", the slot "class*"
points to the package name if "new" was called on a named class, or the object if "new" was called on an
object.
The value of this slot can be returned quite easily like so:
$foo->reflect->class;
Calling Inherited Methods
Methods (and fields) inherited from prototypes or classes are not generally available using the usual
Perl "$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".
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.
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.
Class::Prototyped" Methods
new() - Construct a new "Class::Prototyped" object.
A new object is created. If this is called on a class or object 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.
When called on named classes, either via the package name or via the object (i.e.
"MyPackage->reflect->object()"), "class*" is set to the package name. When called on an object, "class*"
is set to the object on which "new" was called.
The passed arguments are handed off to "addSlots".
Note that "new" calls "newCore", so if you want to override "new", but want to ensure that your changes
are applicable to "newPackage", "clone", and "clonePackage", you may wish to override "newCore".
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,
);
The following will create a new object that inherits behavior from $bar with one field slot, "field1",
and one parent slot, "class*", that points to $bar.
my $foo = $bar->new(
field1 => 123,
);
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. This creates a named class. The same behavioral rules for "class*" described above
for "new" apply to "newPackage" (in fact, "new" calls "newPackage").
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 = $p1->clone(
sub1 => sub { print "this is sub1 in p2" },
);
It calls "newCore" to create the new object*, so if you have overridden "new", you should contemplate
overriding "clone" in order to ensure that behavioral changes made to "new" that would be applicable to
"clone" are implemented. Or simply override "newCore".
clonePackage()
Just like "clone", but instead of creating the new object with an arbitrary package name (actually, not
entirely arbitrary - it's generally based on the hash memory address), the first argument is used as the
name of the package. This creates a named class.
If the package name is already in use, this method will croak.
newCore()
This implements the core functionality involved in creating a new object. The first passed parameter
will be the name of the caller - either "new", "newPackage", "clone", or "clonePackage". The second
parameter is the name of the package if applicable (i.e. for "newPackage" and "clonePackage") calls,
"undef" if inapplicable. The remainder of the parameters are any slots to be added to the newly created
object/package.
If called with "new" or "newPackage", the "class*" slot will be prepended to the slot list if applicable.
If called with "clone" or "clonePackage", all slots on the receiver will be prepended to the slot list.
If you wish to add behavior to object instantiation that needs to be present in all four of the
instantiators (i.e. instance tracking), it may make sense to override "newCore" so that you implement the
code in only one place.
reflect() - Return a mirror for the object or class
The structure of an object is modified by using a mirror. This is the equivalent of calling:
Class::Prototyped::Mirror->new($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 "$self->reflect->super('destroy');" at some point in
the code.
Here is a quick overview of the default destruction behavior for objects:
• "Class::Prototyped::DESTROY" is called because it is linked into the package for all objects at
instantiation time
• All no longer existent entries are stripped from @ISA
• The inheritance hierarchy is searched for a "DESTROY" method that is not
"Class::Prototyped::DESTROY". This "DESTROY" method is stashed away for a later call.
• The inheritance hierarchy is searched for a "destroy" method and it is called. Note that the
"Class::Prototyped::destroy" method, which will either be called directly because it shows up in the
inheritance hierarchy or will be called indirectly through calls to
"$self->reflect->super('destroy');", will delete all non-parent slots from the object. It leaves
parent slots alone because the destructors for the parent slots should not be called until such time
as the destruction of the object in question is complete (otherwise inherited destructors might still
be executing, even though the object to which they belong has already been destroyed). This means
that the destructors for objects referenced in non-parent slots may be called, temporarily
interrupting the execution sequence in "Class::Prototyped::destroy".
• The previously stashed "DESTROY" method is called.
• The parent slots for the object are finally removed, thus enabling the destructors for any objects
referenced in those parent slots to run.
• Final "Class::Prototyped" specific cleanup is run.
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:
• $slotType can be omitted. In this case, the slot's type will be determined by inspecting the slot's
name (to determine if it is a parent slot) and the slot's value (to determine whether it is a field
or method slot). The $slotType value can, however, be used to supply a reference to a code object as
the value for a field slot. Note that this means that "FIELD", "METHOD", and "PARENT" are not legal
attribute names (since this would make parsing difficult).
• If there is only one attribute and if the value is 1, then the value can be omitted.
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)
Stores profiling information in $Class::Prototyped::Mirror::PROFILE::counts. If "profile" is set
to 1, increments "$counts->{$package}->{$slotName}" everytime the slot is accessed. If "profile"
is set to 2, increments "$counts->{$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:
• 'default' - the extended slot syntax and the slot value are returned
• 'simple' - the slot name and the slot value are returned. Note that in this mode, there is no access
to any attributes the slot may have
• 'rotated' - the slot name and the following hash are returned like so:
$slotName => {
attribs => %slotAttribs,
type => $slotType,
value => $slotValue
},
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().
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.
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.
SEE ALSO
Class::SelfMethods
Class::Object
Class::Classless
perl v5.40.0 2024-09-30 Class::Prototyped(3pm)