Skip to content


Subversion checkout URL

You can clone with
Download ZIP
Tag: php-5.3.6RC1
Fetching contributors…

Cannot retrieve contributors at this time

1167 lines (898 sloc) 36.3 KB
Changes in the Zend Engine 2.0
* New Object Model.
The Zend Engine's handling of objects has been completely
changed in order to allow for new features, but also to increase
its performance.
Objects were handled in previous versions like primitive types
(for instance integers and strings). The drawback of this method
is, that semantically the whole object was copied when a
variable was assigned or parameters were passed to a method. The
new approach refers to objects by handle and not by value (one
can think of a handle as an object's ID).
Many PHP programmers aren't even aware of the copying quirks of
the old object model and, therefore, there is a relatively good
chance that the amount of PHP applications that will work out of
the box or after a very small amount of modifications would be
* $this
Unlike in Zend Engine 1 the pseudo variable $this cannot be
exchanged in Zend Engine 2. You can of course modify or work with
an object by using $this but you cannot replace $this with another
object to change the original object.
class Foo {
function replace($other)
$this = $other;
$object = new Foo;
$object->prop = 'Hello';
$other = new Foo;
$other->prop = 'Bye';
print $object->prop; // still shows 'Hello'
Zend Engine 2.0 will issue a compile error, if an assignment
to $this is found.
* Private and Protected Members.
The Zend Engine 2.0 introduces private and protected member
variables. Note that for performance reasons no error message is
emitted in case of an illegal access to a private or protectecd
member variable.
class MyClass {
private $Hello = "Hello, World!\n";
protected $Bar = "Hello, Foo!\n";
protected $Foo = "Hello, Bar!\n";
function printHello() {
print "MyClass::printHello() " . $this->Hello;
print "MyClass::printHello() " . $this->Bar;
print "MyClass::printHello() " . $this->Foo;
class MyClass2 extends MyClass {
protected $Foo;
function printHello() {
MyClass::printHello(); /* Should print */
print "MyClass2::printHello() " . $this->Hello; /* Shouldn't print out anything */
print "MyClass2::printHello() " . $this->Bar; /* Shouldn't print (not declared)*/
print "MyClass2::printHello() " . $this->Foo; /* Should print */
$obj = new MyClass();
print $obj->Hello; /* Shouldn't print out anything */
print $obj->Bar; /* Shouldn't print out anything */
print $obj->Foo; /* Shouldn't print out anything */
$obj->printHello(); /* Should print */
$obj = new MyClass2();
print $obj->Hello; /* Shouldn't print out anything */
print $obj->Bar; /* Shouldn't print out anything */
print $obj->Foo; /* Shouldn't print out anything */
Protected member variables can be accessed in classes extending the
class they are declared in, whereas private member variables can
only be accessed by the class they belong to.
* Private and protected methods.
The Zend Engine 2.0 introduces private and protected methods.
class Foo {
private function aPrivateMethod() {
echo "Foo::aPrivateMethod() called.\n";
protected function aProtectedMethod() {
echo "Foo::aProtectedMethod() called.\n";
class Bar extends Foo {
public function aPublicMethod() {
echo "Bar::aPublicMethod() called.\n";
$o = new Bar;
Old code that has no user-defined classes or functions named
'public', 'protected' or 'private' should run without modifications.
* Abstract Classes and Methods.
The Zend Engine 2.0 introduces abstract classes and methods. An
abstract method only declares the method's signature and does not
provide an implementation. A class that contains abstract methods
needs to be declared abstract.
abstract class AbstractClass {
abstract public function test();
class ImplementedClass extends AbstractClass {
public function test() {
echo "ImplementedClass::test() called.\n";
$o = new ImplementedClass;
Classes that do not have abstract methods can be declared abstract
to prevent them from being instantiated.
Old code that has no user-defined classes or functions named
'abstract' should run without modifications.
* Interfaces.
The Zend Engine 2.0 introduces interfaces. A class may implement
an arbitrary list of interfaces.
interface Printable {
public function dump();
class PrintableExample implements Printable {
public function dump() {
// ...
Old code that has no user-defined classes or functions named
'interface' or 'implements' should run without modifications.
An interface may extend one or more base interfaces (but not
implement them). Neither a class nor an interface can inherit
methods of the same name from different root interfaces.
Interfaces may contain abstract static methods.
interface Printable {
function dump();
interface Streamable extends Printable {
function writeToStream();
static function readFromStream();
class PrintableExample implements Streamable {
public function dump() {
// ...
function writeToStream() {
// ...
static function readFromStream() {
// ...
A class that does not implement all interface methods must be
declared as an abstract class.
* Class Type Hints.
While remaining loosely typed the Zend Engine 2.0 introduces the
ability to use class type hints to declare the expected class of
objects that are passed as parameters to a method.
interface Foo {
function a(Foo $foo);
interface Bar {
function b(Bar $bar);
class FooBar implements Foo, Bar {
function a(Foo $foo) {
// ...
function b(Bar $bar) {
// ...
$a = new FooBar;
$b = new FooBar;
These class type hints are not checked upon compilation, as would
be the case in a typed language, but during runtime.
This means that
function foo(ClassName $object) {
// ...
is equivalent to
function foo($object) {
if (!($object instanceof ClassName)) {
die('Argument 1 must be an instance of ClassName');
This syntax only applies to objects/classes, not built-in types.
* Final methods and classes.
The Zend Engine 2.0 introduces the "final" keyword to declare
final methods. Those cannot be overridden by sub-classes.
class Foo {
final function bar() {
// ...
It is furthermore possible to make a class final. Doing this
prevents a class from being specialized (it cannot be inherited
by another class). There's no need to declare the methods of
a final class themselves as final.
final class Foo {
// class definition
// the next line is impossible
// class Bork extends Foo {}
Properties cannot be final. See per-class constants below.
Old code that has no user-defined classes or functions named
'final' should run without modifications.
* Object Cloning.
The Zend Engine 1.0 offered no way a user could decide what copy
constructor to run when an object is duplicated. During
duplication, the Zend Engine 1.0 did a bitwise copy making an
identical replica of all the object's properties.
Creating a copy of an object with fully replicated properties is
not always the wanted behavior. A good example of the need for
copy constructors, is if you have an object which represents a
GTK window and the object holds the resource of this GTK window,
when you create a duplicate you might want to create a new
window with the same properties and have the new object hold the
resource of the new window. Another example is if your object
holds a reference to another object which it uses and when you
replicate the parent object you want to create a new instance of
this other object so that the replica has its own separate copy.
An object copy is created by using the clone operator.
$copy_of_object = clone $object;
When the developer asks to create a new copy of an object, the
Zend Engine will check if a __clone() method has been defined or
not. If not, it will call a default __clone() which will copy
all of the object's properties. If a __clone() method is
defined, then it will be responsible to set the necessary
properties in the created object. For convenience, the engine
ensures, that the clone will be initialized with all of the
properties from the source object, so that developers can start
with a by-value replica of the source object, and only override
properties that need to be changed.
class MyCloneable {
static $id = 0;
function MyCloneable() {
$this->id = self::$id++;
function __clone() {
$this->address = 'New York';
$this->id = self::$id++;
$obj = new MyCloneable();
$obj->name = 'Hello';
$obj->address = 'Tel-Aviv';
$obj_clone = clone $obj;
print $obj->id . "\n";
print $obj->name . "\n";
print $obj->address . "\n";
print $obj_clone->id . "\n";
print $obj_clone->name . "\n";
print $obj_clone->address . "\n";
* Unified Constructors.
The Zend Engine allows developers to declare constructor methods
for classes. Classes which have a constructor method call this
method on each newly-created object, so it is suitable for any
initialization that the object may need before it can be used.
With the Zend Engine 1.0, constructor methods were class methods
that had the same name as the class itself. Since it is very
common to call parent constructors from derived classes, the way
the Zend Engine 1.0 worked made it a bit cumbersome to move
classes around in a large class hierarchy. If a class is moved
to reside under a different parent, the constructor name of that
parent changes as well, and the code in the derived class that
calls the parent constructor has to be modified.
The Zend Engine 2.0 introduces a standard way of declaring
constructor methods by calling them by the name __construct().
class BaseClass {
function __construct() {
print "In BaseClass constructor\n";
class SubClass extends BaseClass {
function __construct() {
print "In SubClass constructor\n";
$obj = new BaseClass();
$obj = new SubClass();
For backwards compatibility, if the Zend Engine 2.0 cannot find
a __construct() function for a given class, it will search for
the old-style constructor function, by the name of the class.
Effectively, it means that the only case that would have
compatibility issues is if the class had a method named
__construct() which was used for different semantics.
* Destructors.
Having the ability to define destructors for objects can be very
useful. Destructors can log messages for debugging, close
database connections and do other clean-up work.
No mechanism for object destructors existed in the Zend Engine
1.0, although PHP had already support for registering functions
which should be run on request shutdown.
The Zend Engine 2.0 introduces a destructor concept similar to
that of other object-oriented languages, such as Java: When the
last reference to an object is destroyed the object's
destructor, which is a class method name __destruct() that
recieves no parameters, is called before the object is freed
from memory.
class MyDestructableClass {
function __construct() {
print "In constructor\n";
$this->name = 'MyDestructableClass';
function __destruct() {
print 'Destroying ' . $this->name . "\n";
$obj = new MyDestructableClass();
Like constructors, parent destructors will not be called
implicitly by the engine. In order to run a parent destructor,
one would have to explicitly call parent::__destruct() in the
destructor body.
* Constants.
The Zend Engine 2.0 introduces per-class constants.
class Foo {
const constant = 'constant';
echo 'Foo::constant = ' . Foo::constant . "\n";
Old code that has no user-defined classes or functions
named 'const' will run without modifications.
* Exceptions.
The Zend Engine 1.0 had no exception handling. The Zend Engine 2.0
introduces a exception model similar to that of other programming
languages. But there is no catch all and no finally clause.
Old code that has no user-defined classes or functions 'catch',
'throw' and 'try' will run without modifications.
Exceptions can be rethrown in catch blocks. Also it is possible to
have multiple catch blocks. In that case the caught exception is
compared with the classtype of each catch block from top to bottom
and the first block that has a 'instanceof' match gets executed.
When the catch block finishes execution continues at the end of
the last catch block. If no catch block has a 'instanceof' match
then the next try/catch block is searched until no more try/catch
blocks are available. In that case the exception is an uncaught
exception and the program terminates with showing the exception.
class MyException {
function __construct($exception) {
$this->exception = $exception;
function Display() {
print "MyException: $this->exception\n";
class MyExceptionFoo extends MyException {
function __construct($exception) {
$this->exception = $exception;
function Display() {
print "MyException: $this->exception\n";
try {
throw new MyExceptionFoo('Hello');
catch (MyException $exception) {
catch (Exception $exception) {
echo $exception;
Even though the above example shows that it is possible to define
exception classes that don't inherit from Exception it is best to
do so. This is because the internal Exception class can gather a
lot of information otherwise not available. The PHP code emulation
code would look something like shown below. The comments show the
meaning of each property. As the code shows it is possible to read
any available information by using the getter methods. But since
some of the methods are used internally they are marked final. All
in all the class is very restrictive because it must be ensured
that anything used internally always works as expected.
Emulating class Exception:
class Exception {
function __construct(/*string*/ $message=NULL, /*int*/ $code=0) {
if (func_num_args()) {
$this->message = $message;
$this->code = $code;
$this->file = __FILE__; // of throw clause
$this->line = __LINE__; // of throw clause
$this->trace = debug_backtrace();
$this->string = StringFormat($this);
protected $message = 'Unknown exception'; // exception message
protected $code = 0; // user defined exception code
protected $file; // source filename of exception
protected $line; // source line of exception
private $trace; // backtrace of exception
private $string; // internal only!!
final function getMessage() {
return $this->message;
final function getCode() {
return $this->code;
final function getFile() {
return $this->file;
final function getTrace() {
return $this->trace;
final function getTraceAsString() {
return self::TraceFormat($this);
function _toString() {
return $this->string;
static private function StringFormat(Exception $exception) {
// ... a function not available in PHP scripts
// that returns all relevant information as a string
static private function TraceFormat(Exception $exception) {
// ... a function not available in PHP scripts
// that returns the backtrace as a string
If you derive your exception classes from this Exception base class
your exceptions will be nicely shown in the builtin handler for
uncaught exceptions.
Note: The method getMessage() is a final read only access method to
the private proeprty message that is set in the constructor. If you
feel a need to overwrite the exception display then overload method
__toString() in your derived class or implement your own extneral
exception display function to accomplish your desired formatting.
function display_exception(Exception $ex)
echo 'Exception: ' . $ex->getMessage() . 'with backtrace: <pre>';
echo $ex->getTrace();
echo '</pre>';
// your code here
catch (Exception $ex)
* Dereferencing objects returned from functions.
class Circle {
function draw() {
print "Circle\n";
class Square {
function draw() {
print "Square\n";
function ShapeFactoryMethod($shape) {
switch ($shape) {
case 'Circle': return new Circle();
case 'Square': return new Square();
* Member variables of classes can now be initialized.
class foo {
static $my_static = 5;
public $my_prop = 'bla';
print foo::$my_static;
$obj = foo;
print $obj->my_prop;
* Static Methods.
The Zend Engine 2.0 introduces the 'static' keyword to declare
a method static, thus callable from outside the object context.
class Foo {
public static function aStaticMethod() {
// ...
The pseudo variable $this is not available inside a method that
has been declared static.
* instanceof.
New support for an instanceof operator which checks if an object
is of a certain class or interface type.
class Foo {
$obj = new Foo();
if ($obj instanceof Foo) {
print "Yay!\n";
* Parameters that are passed by reference to a function
may now have default values.
function my_function(&$var = null) {
if ($var === null) {
die('$var needs to have a value');
* __autoload().
The __autoload() interceptor function will be automatically called
when an undeclared class is to be instantiated. The name of that
class will be passed to the __autoload() interceptor function as its
only argument. __autoload() must succeed in loading the class. If it
doesn't then an E_ERROR is emitted.
function __autoload($className) {
include_once $className . '.php';
$object = new ClassName;
* Method calls and property accesses can be overloaded
by class methods __call(), __get() and __set().
__get() and __set() Example:
class Setter {
public $n;
public $x = array('a' => 1, 'b' => 2, 'c' => 3);
function __get($nm) {
print "Getting [$nm]\n";
if(isset($this->x[$nm])) {
$r = $this->x[$nm];
print "Returning: $r\n";
return $r;
} else {
print "Nothing!\n";
function __set($nm, $val) {
print "Setting [$nm] to $val\n";
if(isset($this->x[$nm])) {
$this->x[$nm] = $val;
print "OK!\n";
} else {
print "Not OK!\n";
$foo = new Setter();
$foo->n = 1;
$foo->a = 100;
__call() Example:
class Caller {
var $x = array(1, 2, 3);
function __call($m, $a) {
print "Method $m called:\n";
return $this->x;
$foo = new Caller();
$a = $foo->test(1, '2', 3.4, true);
* Iteration
Objects may be iterated in an overloaded way when used with
foreach. The default behavior is to iterate over all properties
with respect to property visibility.
class Foo {
var $x = 1;
var $y = 2;
$obj = new Foo;
foreach ($obj as $prp_name => $prop_value) {
// using the property
Each class whose instances can be iterated with foreach should
implement the empty interface 'Traversable'. Hence any object
that says it implements 'Traversable' can be used with foreach.
The interfaces 'IteratorAggregate' and 'Iterator' allow to specify
how class objects are iterated in PHP code. The first of them simply
has a method 'getIterator' which must return an object that either
implements the interface 'Iterator' or is instantiated from an
internal class that can be iterated.
class ObjectIterator implements Iterator {
private $obj;
private $num;
function __construct($obj) {
$this->obj = $obj;
function rewind() {
$this->num = 0;
function valid() {
return $this->num < $this->obj->max;
function key() {
return $this->num;
function current() {
switch($this->num) {
case 0: return "1st";
case 1: return "2nd";
case 2: return "3rd";
default: return $this->num."th";
function next() {
class Object implements IteratorAggregate {
public $max = 3;
function getIterator() {
return new ObjectIterator($this);
$obj = new Object;
// this foreach ...
foreach($obj as $key => $val) {
echo "$key = $val\n";
// matches the following 7 lines with the for directive.
$it = $obj->getIterator();
for($it->rewind(); $it->valid(); $it->next()) {
$key = $it->key();
$val = $it->current();
echo "$key = $val\n";
The matching for directive is very intersting here since it shows
the use of all abstract methods declared in the interfaces Iterator
and IteratorAggregate respectively.
* Array overloading
Objects can be used with Array notation when they implement the
interface ArrayAccess. You cannot use such objects in standard
array functions, however you have full control over the array
notation. This allows lazy initialization or read only array.
Note that setting [] results in a call to offsetSet() with
index being NULL. That means that as with standard arrays you
cannot store NULL keys.
class ArrayClass implements ArrayAccess {
public $a = array();
function offsetExists($index) {
return array_key_exists($index, $this->a);
function offsetGet($index) {
return $this->a[$index];
function offsetSet($index, $newval) {
return $this->a[$index] = $newval;
function offsetUnset($index) {
$obj = new ArrayClass;
$obj[0] = 'bla'; // calls offsetSet(0,'bla')
$obj[] = 42; // calls offsetSet(NULL, 42)
$x = $obj[0]; // calls offsetGet(0)
$b = isset($obj[0]); // calls offsetExists(0)
unset($obj[0]); // calls offsetUnset(0)
* __METHOD__
The pseudo constant __METHOD__ shows the current class and method
when used inside a method and the function when used outside of a
class Foo {
function Show() {
echo __FILE__ . '(' . __LINE__ . ')' . __METHOD__;
function Test() {
echo __FILE__ . '(' . __LINE__ . ')' . __METHOD__;
* __toString()
The magic method __toString() allows to overload the object to
string conversion. This conversion is only done automatically for
the printing functions (echo, print) but not for other functions
that expect strings. Also the function __toString is not used in
places where objects are not allowed but strings are like array
indices. Note that specialized objects may be converted to a string
in any place but without calling __toString().
class Foo {
function __toString() {
return "What ever";
$obj = new Foo;
$str = (string) $obj; // call __toString()
echo $obj; // call __toString()
$ar = array();
$ar[(string)$obj]; // this works
$ar[$obj]; // this is not allowed
* Reflection API
PHP 5 comes with a complete Reflection API that adds the ability to
reverse-engineer classes, interfaces, functions and methods as well
as extensions.
The Reflection API also offers ways of getting doc comments for
functions, classes and methods.
Nearly all aspects of object oriented code can be reflected by
using the Reflection API which is documented separately:
class Foo {
public $prop;
function Func($name) {
echo "Hello $name";
ReflectionObject::export(new Foo);
ReflectionMethod::export('Foo', 'func');
ReflectionProperty::export('Foo', 'prop');
* New memory manager
The Zend Engine has a new memory manager which allows it to run efficiently
in multi-threaded environments as it doesn't need to use mutexes to lock
and unlock during allocation/deallocation.
* Others
Probably other changes which we forgot to list. This list will be kept up-to-date
as much as possible.
Changes in the Zend Engine 1.0
The Zend Engine was designed from the ground up for increased speed,
reduced memory consumption and more reliable execution. We dare say
it meets all of these goals and does so pretty well. Beyond that,
there are several improvements in the language engine features:
* References support.
$foo = &$a; would make $foo and $a be two names to the same
variable. This works with arrays as well, on either side; e.g.,
$foo = &$a[7]; would make $foo and $a[7] be two names to the
same variable. Changing one would change the other and vice
* Object overloading support.
This feature allows various OO libraries to use the OO notation
of PHP to access their functionality. Right now, no use is made
of that feature, but we'd have a COM module ready by the time
PHP 4.0 is released. A CORBA module would probably follow.
* include() and eval() are now functions, and not statements.
That means they return a value. The default return value from
include() and eval() is 1, so that you can do if (include())
without further coding. The return value may be changed by
returning a value from the global scope of the included file or
the evaluated string. For example, if 'return 7;' is executed in
the global scope of, include('') would evaluate
to 7.
* Automatic resource deallocation.
Several people have been bitten by the fact that PHP 3.0 had no
concept of reference counting. The Zend Engine adds full
reference counting for every value in the system, including
resources. As soon as a resource is no longer referenced from
any variable, it is automatically destroyed to save memory and
resources. The most obvious example for the advantage in this is
a loop that has an SQL query inside it, something like '$result
= sql_query(...);'. In PHP 3.0, every iteration resulted in
another SQL result-set allocated in the memory, and all of the
result sets weren't destroyed until the end of the script's
execution. With the Zend Engine, as soon as we overwrite an old
result set with a new one, the old result set which is no longer
referenced, is destroyed.
* Full support for nesting arrays and objects within each other,
in as many levels as you want.
* true and false are now constants of type boolean.
Comparing any other value to them would convert that value to a
boolean first, and conduct the comparison later. That means, for
example, that 5==true would evaluate to true (in PHP 3.0, true
was nothing but a constant for the integer value of 1, so
5==true was identical to 5==1, which was false).
* Runtime binding of function names.
This complex name has a simple explanation - you can now call
functions before they're declared!
* Added here-docs support.
* Added foreach.
Two syntaxes supported:
foreach(array_expr as $val) statement
foreach(array_expr as $key => $val) statement
* A true unset() implementation.
A variable or element that is unset(), is now sent to oblivion
in its entirely, no trace remains from it.
* Output buffering support.
Use ob_start() to begin output buffering, ob_end_flush() to end
buffering and send out the buffered contents, ob_end_clean() to
end buffering without sending the buffered contents, and
ob_get_contents() to retreive the current contents of the output
buffer. Header information (header(), content type, cookies) are
not buffered. By turning on output buffering, you can
effectively send header information all throughout your file,
regardless of whether you've emitted body output or not.
* Full variable reference within quoted strings:
${expr} - full indirect reference support for scalar
{variable} - full variable support
For example:
$foo[5]['bar'] = 'foobar';
print "{$foo[5]["bar"]}"; // would print "foobar"
* Ability to call member functions of other classes from within
member functions or from the global scope.
You can now, for example, override a parent function with a
child function, and call the parent function from it.
* Runtime information for classes (class name, parent, available
functions, etc.).
* Much more efficient syntax highlighter - runs much quicker,
performs more reliably, and generates much tighter HTML.
* A full-featured debugger has been integrated with the language
(supports breakpoints, expression evaluation, step-in/over,
function call backtrace, and more).
The Zend Engine claims 100% compatability with the engine of PHP
3.0, and is shamelessly lying about it. Here's why:
* Static variable initializers only accept scalar values
(in PHP 3.0 they accepted any valid expression). The impact
should be somewhere in between void and non existent, since
initializing a static variable with anything but a simple
static value makes no sense at all.
* The scope of break and continue is local to that of an
include()'d file or an eval()'d string. The impact should
be somewhat smaller of the one above.
* The return statement no longer works from a require()'d file. It
hardly worked in PHP 3.0, so the impact should be fairly small. If
you want this functionality - use include() instead.
* unset() is no longer a function, but a statement.
* The following letter combination is not supported within
encapsulated strings: "{$". If you have a string that includes
this letter combination, for example, print "{$somevar"; (which
printed the letter { and the contents of the variable $somevar in
PHP 3.0), it will result in a parse error with the Zend Engine.
In this case, you would have to change the code to print
"\{$somevar"; This incompatability is due to the full variable
reference within quoted strings feature added in the Zend
Jump to Line
Something went wrong with that request. Please try again.