Differences Between PHP 4 and 5 - By: luudanh123

• PHP 5 allows limited type hinting. This allows you to specify that the param-
  eter to a function or class method can only be of a speciï¬Â�c class (or one of its
  subclasses), or an array. However, youmay not specify any other scalar types.
  The foreach construct now supports by-reference declaration of the value ele-
  ment.


• A number of newfunctions, particularly for string and arraymanipulation, has
  also been added to the core platform.

• For all intents and purposes, all objects in PHP 5 are passed by reference. This
  means that assigning an object to a variable will not create a copy of the for-
  mer, but simply creates another reference to it.


• Constants, aswell as staticmethods and properties, can nowbe deï¬Â�nedwithin
  the scope of a class.


• Class methods and properties now feature visibility, and can be declared as
  public, private or protected. Classes and methods can also be declared as
  final to prevent further inheritance.


• Since all objects are assigned by reference, you now need a specializedmecha-
  nismto copy objects. This is provided by the clone construct and the __clone()
  magicmethod.


• PHP 5 features uniï¬Â�ed constructors and destructors-all constructors should
  now be named __construct(), and the new __destruct() magic method has
  been added for object destruction.


• With the addition of interfaces and abstract classes, PHP developers now have
  far greater control over how they implement their object-oriented code. In-
  terfaces can be used to deï¬Â�ne common APIs, while abstract classes provide
  models for class implementations that follow a speciï¬Â�c blueprint.


• Class deï¬Â�nitions can now be loaded on demand by using the __autoload()
  function.

• __get() and __set() are called when accessing or assigning an undeï¬Â�ned ob-
  ject property, while __call() is executed when calling a non-existent method
  of a class.


• __isset() is called when passing an undeï¬Â�ned property to the isset() con-
  struct.


• __unset() is called when passing an undeï¬Â�ned property to unset().


• __toString() is called when trying to directly echo or print() an object.


• __set_state() is inserted dynamically by var_export() to allow for re-
  initialization on execution of var_export()'s output.

• SimpleXML allows easy access to XML data using object and array notation.


• PHP 5 also introduces a DOMXML, DOMXSL and Sablotron replacement in
  the formof the libxml2-based DOMand XSL extensions.


• The PHP Data Objects (PDO) extension provides a uniï¬Â�ed database access ex-
  tension that allows access to many different types of database systems by us-
  ing a common interface. PDO is not an abstraction layer-except for prepared
  queries, it does nothing to abstract the actual database code (SQL), itself.


• The hash extension is a newreplacement for theGPLed libmhash; itwas added
  to the PHP core starting with version 5.1.2. It can produce hashes using many
  algorithms, including the familiarMD5 and SHA1, aswell as somemore secure
  (albeit slower) algorithms, such as snefru.


• The Standard PHP Library (SPL) provides numerous interfaces that enhance
  the way classes interact with the PHP language, including the new Iterator
  interfaces.


• The new Reï¬'ection extension allows for runtime introspection of executing
  PHP code.

• Classes now support exceptions; the new set_exception_handler() function
  allows you to deï¬Â�ne a script-wide exception handler.


• The E_STRICT error reporting level has been added to the language to emit no-
  tices when legacy or deprecated code is encountered

About the Author

Luu Danh, MyWayE, Ltd, has more than 5 years of experience in technology writing and web site development. you can also check out his latest website on Fun Girls Games or view Pregnancy FAQ. Thank you.

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