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Monday, August 25, 2008

PHP OOP

New Functionality
Support for PPP Exceptions Object Iteration Object Cloning Interfaces Autoload And much more, and it is faster too!

The Basics
The basic object operations have not changed since PHP 4.
class my_obj { var $foo; function my_obj() { // constructor $this->foo = 123; } function static_method($a) { return urlencode($a); } } $a = new my_obj; // instantiate an object $a->my_obj(); // method calls my_obj::static_method(123); // static method call

Similar, but not the same.
While the syntax remains the same, internals are quite different.  Objects are now always being passed by reference, rather then by value.
PHP 5 $a = new foo(); == PHP4 $a = &new foo();

While the old style constructors are supported, new more consistent mechanism is available. __construct() method.

PPP Annoyance
The VAR keyword for identifying class properties became deprecated and will throw an E_STRICT warning.
PHP Strict Standards: var: Deprecated. Please use the public/private/protected modifiers in obj.php on line 3.

Instead, you should use PUBLIC, PRIVATE or PROTECTED keywords.

PHP 5 Ready Code
foo = 123; } // static methods need to be declared as static // to prevent E_STRICT warning messages. static function static_method($a) { return urlencode($a); } } $a = new my_obj; my_obj::static_method("a b"); ?>

PHP 5 Constructors
In PHP 5 parent::__construct will automatically determine what parent constructor is available and call it.
class main { function main() { echo "Main Class\n"; } } class child extends main { function __construct() { parent::__construct(); echo "Child Class\n"; } } $a = new child;

Destructors
Destructor methods specifies code to be executed on object de-initialization.
class fileio { private $fp; function __construct ($file) { $this->fp = fopen($file, "w"); } function __destruct() { // force PHP to sync data in buffers to disk fflush($this->fp); fclose($this->fp); } }

Objects by Reference
No matter how an object is passed in PHP 5+, you always work with the original.
function foo($obj) { $obj->foo = 1; } $a = new StdClass; foo($a); echo $a->foo; // will print 1 class foo2 { function __construct() { $GLOBALS['zoom'] = $this; $this->a = 1; } } $a = new foo2(); echo ($a->a == $zoom->a); // will print 1

What If I Want a Copy?
To copy an object in PHP 5 you need to make use of the clone keyword.  This keyword does the job that $obj2 = $obj; did in PHP 4.

Choices Choices Choices
Being a keyword, clone supports a number of different, but equivalent syntaxes.
class A { public $foo; } $a = new A; $a_copy = clone $a; $a_another_copy = clone($a); $a->foo = 1; $a_copy->foo = 2; $a_another_copy->foo = 3; echo $a->foo . $a_copy->foo . $a_another_copy->foo; // will print 123

Extending Clone
__clone() can be extended to further modify the newly made copy.
class A { public $is_copy = FALSE; public function __clone() { $this->is_copy = TRUE; } } $a = new A; $b = clone $a; var_dump($a->is_copy, $b->is_copy); // false, true

PPP
Like in other OO languages, you can now specify the visibility of object properties, for the purposes of restricting their accessibility.
PUBLIC – Accessible to all.  PROTECTED – Can be used internally and inside extending classes.  PRIVATE – For class’ internal usage only.

PPP in Practice
a . $this->b . $this->c; } } class miniSample extends sample { function __construct() { echo $this->a . $this->b . $this->c; } } $a = new sample(); // will print 123 $b = new miniSample(); // will print 13 & notice about undefined property miniSample::$b echo $a->a . $a->b . $a->c; // fatal error, access to private/protected property ?>

Practical PPP Applications
$v) { if (isset($_POST[$k])) { $a->$k = $_POST[$k]; } } ?>

Not all PHP functions/constructs respect, PPP visibility rules

Static Properties
Another new feature of PHP 5 objects, is the ability to contain static properties.
login; // undefined property warning $a->login = "Local Value"; // parse error? (NOPE!) echo $a->login; // will print "Local Value" ?>

Class Constants
PHP 5 also supports class constants, which are very similar to static properties, however their values can never be altered.
class cc { const value = 'abc 123'; function print_constant() { // access class constants inside of the class echo self::value; } } echo cc::value; // access class constants outside of the class

PPP Applies to Methods Too!
Method access can also be restricted via PPP.
Hide and prevent access to application’s internal functionality.  Data separation.  Increased security. Cleaner Code.

Practical PPP Methods
class mysql { private $login, $pass, $host; protected $resource, $error, $qp; private function __construct() { $this->resource = mysql_connect($this->host, $this->login, $this->pass); } protected function exec_query($qry) { if (!($this->qp = mysql_query($qry, $this->resource))) { self::sqlError(mysql_error($this->resource)); } } private static function sqlError($str) { open_log(); write_to_error_log($str); close_log(); } }

Practical PPP Methods
class database extends mysql { function __construct() { parent::__construct(); } function insert($qry) { $this->exec_query($qry); return mysql_insert_id($this->resource); } function update($qry) { $this->exec_query($qry); return mysql_affected_rows($this->resource); } }

Final
PHP 5 allows classed and methods to be defined a FINAL.
For methods it means that they cannot be overridden by a child class.  Classes defined as final cannot be extended.

Final Method Example
By making a method FINAL you prevent and extending classes from overriding it. Can be used to prevent people from re-implementing your PRIVATE methods.
class main { function foo() {} final private function bar() {} } class child extends main { public function bar() {} } $a = new child();

Final Class Example
Classes declared as final cannot be extended.
final class main { function foo() {} function bar() {} } class child extends main { } $a = new child();
PHP Fatal error: Class child may not inherit from final class (main)

Autoload
Maintaining class decencies in PHP 5 becomes trivial thanks to the __autoload() function.

If defined, the function will be used to automatically load any needed class that is not yet defined.

Magic Methods
Objects in PHP 5 can have 3 magic methods.
__sleep() – that allows scope of object serialization to be limited. (not new to PHP)  __wakeup() – restore object’s properties after deserialization.  __toString() – object to string conversion mechanism.

Serialization
Serialization is a process of converting a PHP variable to a specially encoded string that can then be used to recreate that variable. Needed for complex PHP types such as objects & arrays that cannot simply be written to a file or stored in a database. The serialization process is done via serialize() and restoration of data via unserialize() functions.

Serialize Example
class test { public $foo = 1, $bar, $baz; function __construct() { $this->bar = $this->foo * 10; $this->baz = ($this->bar + 3) / 2; } } $a = serialize(new test()); // encode instantiated class test $b = unserialize($a); // restore the class into $b;

The encoded version of our object looks like this:
O:4:"test":3:{s:3:"foo";i:1;s:3:"bar";i:10;s:3:"baz";d:6.5;}

__sleep()
The __sleep() method allows you to specify precisely which properties are to be serialized.

class test { public $foo = 1, $bar, $baz; function __construct() { $this->bar = $this->foo * 10; $this->baz = ($this->bar + 3) / 2; } function __sleep() { return array('foo'); } }

This makes our serialized data more manageable.
O:4:"test":1:{s:3:"foo";i:1;}

__wakeup()
__wakeup(), if available will be called after deserialization. It’s job is to recreate properties skipped during serialization.
class test { public $foo = 1, $bar, $baz; function __construct() { $this->bar = $this->foo * 10; $this->baz = ($this->bar + 3) / 2; } function __wakeup() { self::__construct(); } }

__toString()
Ever wonder how PHP extensions like SimpleXML are able to print objects and output valid data rather then garbage?
Ilia'); var_dump($xml->data); echo $xml->data; ?>

Output:
object(SimpleXMLElement)#2 (1){ [0]=> string(4) "Ilia" } Ilia

Sample __toString()
foo = rand(); } function __toString() { return (string)$this->foo; } } echo new Sample(); ?>

__toString() Gotchas
Assuming $a = new obj();     echo echo echo echo "str" . $a; "str {$a}" $a{0}; ** (string) $a;

In all of these instances __toString() will not be called.

Overloading
Both method calls and member accesses can be overloaded via the __call, __get and __set methods.  Provide access mechanism to “virtual” properties and methods.

Getter
The getter method, __get() allows read access to virtual object properties.
class makePassword { function __get($name) { if ($name == 'md5') return substr(md5(rand()), 0, 8); else if ($name == 'sha1') return substr(sha1(rand()), 0, 8); else exit(“Invalid Property Name”); } } $a = new makePassword(); var_dump($a->md5, $a->sha1);

Setter
The setter method, __set() allows write access to virtual object properties.

Dynamic Methods
The __call() method in a class can be used to emulate any non-declared methods.
class math { function __call($name, $arg) { if (count($arg) > 2) return FALSE; switch ($name) { case 'add': return $arg[0] + $arg[1]; break; case 'sub': return $arg[0] - $arg[1]; break; case 'div': return $arg[0] / $arg[1]; break; } } }

Important Overloading Reminders
The name passed to __get, __set, __call is not case normalized. $foo->bar != $foo->BAR  Will only be called if the method/property does not exist inside the object.  Functions used to retrieve object properties, methods will not work.  Use with caution, it takes no effort at all to make code terribly confusing and impossible to debug.

Object Abstraction
Abstract classes allow you to create set methods describing the behavior of a to be written class.

Database Abstraction
The methods preceded by abstract keyword must be implemented by the extending classes.
abstract class database { public $errStr = '', $errNo = 0; // these abstract abstract abstract abstract abstract abstract } methods must be provided by extending classes protected function init($login,$pass,$host,$db); protected function execQuery($qry); protected function fetchRow($qryResource); protected function disconnect(); protected function errorCode(); protected function errorNo();

Abstract Implementer
class mysql extends database { private $c; protected function init($login, $pass, $host, $db) { $this->c = mysql_connect($host, $login, $pass); mysql_select_db($db, $this->c); } protected function execQuery($qry) { return mysql_query($qry, $this->c); } protected function fetchRow($res) { return mysql_fetch_assoc($res); } protected function errorCode() {return mysql_error($this->c); } protected function errorNo() { return mysql_errno($this->c); } protected function disconnect() { mysql_close($this->c); } }

Interfaces
Object interfaces allows you to define a method “API” that the implementing classes must provide.

Interface Examples
Interfaces are highly useful for defining a standard API and ensuring all providers implement it fully.
interface webSafe { public function public function } interface sqlSafe { public function public function } encode($str); decode($str);

textEncode($str); binaryEncode($str);

Implementer
A class can implement multiple interfaces.
class safety Implements webSafe, sqlSafe { public function encode($str) { return htmlentities($str); } public function decode($str) { return html_entity_decode($str); } public function textEncode($str) { return pg_escape_string($str); } public function binaryEncode($str) { return pg_escape_bytea($str); } }

ArrayAccess Interface
One of the native interface provided by PHP, allows object to emulate an array.  The interface requires the following :
offsetExists($key) - determine if a value exists  offsetGet($key) - retrieve a value  offsetSet($key, $value) - assign value to a key  offsetUnset($key) - remove a specified value

ArrayAccess in Action
class changePassword implements ArrayAccess { function offsetExists($id) { return $this->db_conn->isValidUserID($id); } function offsetGet($id) { return $this->db_conn->getRawPasswd($id); } function offsetSet($id, $passwd) { $this->db_conn->setPasswd($id, $passwd); } function offsetUnset($id) { $this->db_conn->resetPasswd($id); } } $pwd = new changePassword; isset($pwd[123]); // check if user with an id 123 exists echo $pwd[123]; // print the user’s password $pwd[123] = “pass”; // change user’s password to “pass” unset($pwd[123]); // reset user’s password

Object Iteration
To use it an object  PHP 5 allows an must implement the object to following methods: implement an  rewind internal iterator  current interface that will  key specify exactly how  next an object is to be  valid iterated through.

File Iterator
class fileI Implements Iterator { private $fp, $line = NULL, $pos = 0; function __construct($path) { $this->fp = fopen($path, "r"); } public function rewind() { rewind($this->fp); } public function current() { if ($this->line === NULL) { $this->line = fgets($this->fp); } return $this->line; } }

File Iterator Cont.
public function key() { if ($this->line === NULL) { $this->line = fgets($this->fp); } if ($this->line === FALSE) return FALSE; return $this->pos; } public function next() { $this->line = fgets($this->fp); ++$this->pos; return $this->line; } public function valid() { return ($this->line !== FALSE); }

File Iterator Cont.
$v) { echo "{$k} {$v}"; } ?> 0 1 2 3 4 5 6 7 $v) { echo "{$k} {$v}"; } ?>

Output:
Exceptions
Exceptions are intended as a tool for unifying error handling.  An entire block of code can be encompassed inside a try {} block.  Any errors, are then sent to the catch {} for processing.

Native Exception Class
class Exception { protected $message = 'Unknown exception'; // exception message protected $code = 0; // user defined exception code protected $file; // source filename of exception protected $line; // source line of exception function __construct($message = null, $code = 0); final final final final final final }

function function function function function function

getMessage(); // message of exception getCode(); // code of exception getFile(); // source filename getLine(); // source line getTrace(); // backtrace array getTraceAsString(); // trace as a string

function __toString(); // formatted string for display

Exception Example
getFile(), $e->getLine(), $e->getMessage()); exit; } ?>

Extending Exceptions
class iliaException extends Exception { public function __construct() { parent::__construct($GLOBALS['php_errormsg']); } public function __toString() { return sprintf("Error on [%s:%d]: %s\n", $this->file, $this->line, $this->message); } } ini_set("track_errors", 1); error_reporting(0); try { $fp = fopen("m:/file", "w"); if (!$fp) throw new iliaException; if (fwrite($fp, "abc") != 3) throw new iliaException; if (!fclose($fp)) throw new iliaException; } catch (iliaException $e) { echo $e; }

Stacking & Alternating Exceptions
$a = new dbConnection(); $a->execQuery(); $a->fetchData(); (ConnectException $db) {

} catch (QueryException $qry) { } catch (fetchException $dt) { } ?>

 PHP Exceptions can be stackable or alternate based on the exception name.

Exception Handler
The exception handler function, set_exception_h andler() allows exceptions to be handled without explicitly listing the try {} catch () {} block.
function exHndl($e) { trigger_error($e->getLine()); } set_exception_handler('exHndl'); $fp = fopen("m:/file", "w"); if (!$fp) throw new iliaException; if (fwrite($fp, "abc") != 3) throw new iliaException; if (!fclose($fp)) throw new iliaException;

Type Hinting
While PHP is still type insensitive, you can now specify what type of objects your functions and methods require.

Reflection API
Reflection API provides a mechanism for obtaining detailed information about functions, methods, classes and exceptions.  It also offers ways of retrieving doc comments for functions, classes and methods.

Reflection Mechanisms
The API provides a distinct class for study of different entities that can be analyzed.
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