At first I would like to thank www.docs.php.net for their clear and cool documentation. Recently I’ve gone through the differences in between php4 and php5. I’ve found some interesting things by studying this topic. I think you all should have a look if you want to be a good developer. If you want a better performance and more features in your application easily then this post is appropriate for you. Happy Christmas!!

Type Hinting
PHP 5 introduces Type Hinting. Functions are now able to force parameters to be objects (by specifying the name of the class in the function prototype) or arrays (since PHP 5.1). However, if NULL is used as the default parameter value, it will be allowed as an argument for any later call.

New Object Model
In PHP 5 there is a new Object Model. PHP’s handling of objects has been completely rewritten, allowing for better performance and more features. In previous versions of PHP, objects were handled like primitive types (for instance integers and strings). The drawback of this method was that semantically the whole object was copied when a variable was assigned, or passed as a parameter to a method. In the new approach, objects are referenced by handle, and not by value (one can think of a handle as an object’s identifier).

Many PHP programmers aren’t even aware of the copying quirks of the old object model and, therefore, the majority of PHP applications will work out of the box, or with very few modifications.

List of new Keywords
These words have special meaning in PHP. Some of them represent things which look like functions, some look like constants, and so on–but they’re not, really: they are language constructs. You cannot use any of the following words as constants, class names, function or method names. Using them as variable names is generally OK, but could lead to confusion.You will find detailed documentation on these new keywords by clicking on it.

abstract catch clone final implements interface instanceof namespace private protected public throw try

__NAMESPACE__ __DIR__

Backward Incompatible Changes
Although most existing PHP 4 code should work without changes, you should pay attention to the following backward incompatible changes:

• There are some new reserved keywords.
• strrpos() and strripos() now use the entire string as a needle.
• Illegal use of string offsets causes E_ERROR instead of E_WARNING. An example illegal use is: $str = ‘abc’; unset($str[0]);.
• array_merge() was changed to accept only arrays. If a non-array variable is passed, a E_WARNING will be thrown for every such parameter. Be careful because your code may start emitting E_WARNING out of the blue.
• PATH_TRANSLATED server variable is no longer set implicitly under Apache2 SAPI in contrast to the situation in PHP 4, where it is set to the same value as the SCRIPT_FILENAME server variable when it is not populated by Apache. This change was made to comply with the » CGI specification. Please refer to » bug #23610 for further information, and see also the $_SERVER['PATH_TRANSLATED'] description in the manual. This issue also affects PHP versions >= 4.3.2.
• The T_ML_COMMENT constant is no longer defined by the Tokenizer extension. If error_reporting is set to E_ALL, PHP will generate a notice. Although the T_ML_COMMENT was never used at all, it was defined in PHP 4. In both PHP 4 and PHP 5 // and /* */ are resolved as the T_COMMENT constant. However the PHPDoc style comments /** */, which starting PHP 5 are parsed by PHP, are recognized as T_DOC_COMMENT.
• $_SERVER should be populated with argc and argv if variables_order includes “S”. If you have specifically configured your system to not create $_SERVER, then of course it shouldn’t be there. The change was to always make argc and argv available in the CLI version regardless of the variables_order setting. As in, the CLI version will now always populate the global $argc and $argv variables.
• An object with no properties is no longer considered “empty”.
• In some cases classes must be declared before use. It only happens if some of the new features of PHP 5 (such as interfaces) are used. Otherwise the behaviour is the old.
• get_class(), get_parent_class() and get_class_methods() now return the name of the classes/methods as they were declared (case-sensitive) which may lead to problems in older scripts that rely on the previous behaviour (the class/method name was always returned lowercased). A possible solution is to search for those functions in all your scripts and use strtolower(). This case sensitivity change also applies to the magical predefined constants __CLASS__, __METHOD__, and __FUNCTION__. The values are returned exactly as they’re declared (case-sensitive).
• ip2long() now returns FALSE when an invalid IP address is passed as argument to the function, and no longer -1.
• If there are functions defined in the included file, they can be used in the main file independent if they are before return() or after. If the file is included twice, PHP 5 issues fatal error because functions were already declared, while PHP 4 doesn’t complain about it. It is recommended to use include_once() instead of checking if the file was already included and conditionally return inside the included file.
• include_once() and require_once() first normalize the path of included file on Windows so that including A.php and a.php include the file just once. Read the rest of this entry »