Class::Prototyped(3) User Contributed Perl Documentation Class::Prototyped(3)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 = $p1->clone(
sub1 => sub { print "this is sub1 in p2" },
);
It calls "newCore" to create the new object*, so if you have overriden
"new", you should contemplate overriding "clone" in order to ensure
that behavioral changes made to "new" that would be applicable to
"clone" are implemented. Or simply override "newCore".
clonePackage()
Just like "clone", but instead of creating the new object with an
arbitrary package name (actually, not entirely arbitrary - it's
generally based on the hash memory address), the first argument is used
as the name of the package. This creates a named class.
If the package name is already in use, this method will croak.
newCore()
This implements the core functionality involved in creating a new
object. The first passed parameter will be the name of the caller -
either "new", "newPackage", "clone", or "clonePackage". The second
parameter is the name of the package if applicable (i.e. for
"newPackage" and "clonePackage") calls, "undef" if inapplicable. The
remainder of the parameters are any slots to be added to the newly
created object/package.
If called with "new" or "newPackage", the "class*" slot will be
prepended to the slot list if applicable. If called with "clone" or
"clonePackage", all slots on the receiver will be prepended to the slot
list.
If you wish to add behavior to object instantiation that needs to be
present in all four of the instantiators (i.e. instance tracking), it
may make sense to override "newCore" so that you implement the code in
only one place.
reflect() - Return a mirror for the object or class
The structure of an object is modified by using a mirror. This is the
equivalent of calling:
Class::Prototyped::Mirror->new($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} = $newValue"). This is mostly useful
if you have an object method call that takes parameters, but
you wish to replace it on a given object with a hard-coded
value by using a field (which makes inspecting the value of the
slot through "Data::Dumper" much easier than if you use a
"METHOD" slot to return the constant, since code objects are
opaque).
"autoload" ("filter", rank 50)
The passed value for the "FIELD" slot should be a subroutine
that returns the desired value. Upon the first access, the
subroutine will be called, the return value hard-coded into the
object by adding the slot (including all otherwise specified
attributes), and the value then returned. Useful for
implementing constant slots that are costly to initialize,
especially those that return lists of "Class::Prototyped"
objects!
"profile" ("filter", rank 80)
If "profile" is set to 1, increments
"$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:
· '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 v5.14.1 2011-07-22 Class::Prototyped(3)
