The Reason for PHP 6.0.0 Delay..

The development of PHP 6 has been delayed because the developers have decided the current approach to handling of instance Unicode is not a good one, and are considering alternate ways in the next version of PHP. The updates that were intended for PHP 6 were added to PHP 5.3.0 (namespace support, late static bindings, lambda functions, closures, goto) and 5.4.0 (traits, closure rebinding) instead.

Reasons for Delays to PHP 6

The reasons for the delay to PHP 6 appear to be:

Issues with Unicode support: 

The development team initially decided to use UTF-16 internally in PHP 6. This causes double memory usage for strings, more CPU usage and increased complexity of coding PHP 6. Using UTF-16 apparently took a lot of fun out of developing PHP, caused tension amongst PHP’s developers and slowed development. The choice to use UTF-16 was aborted by Rasmus Lerdorf, creator of PHP, in 2010. The developers restarted the Unicode implementation.

PHP 5.3 took some PHP 6 features: 

PHP 5.3 included many of the features slated as desirable for PHP 6. This removed a lot of momentum for PHP 6.

High Hopes: 

PHP 6 is a major version number change. It’s possible in a major release to make significant changes, including making breaks from the past. Agreeing and delivering major changes can take some time.

Feature Set Not Finalized: 

Agreement hasn’t been reached on the features in PHP 6.0.

Lack of Urgency: 

PHP works very well. There are no burning issues forcing the release of PHP 6.

PHP 5.4 takes some PHP 6 features: 

Rasmus Lerdorf previously stated, when he scrapped PHP 6′s original Unicode implementation, that there may be a PHP 5.4 yet, or PHP may go straight to version 6. Jani Taskinen created a PHP 5.4 development branch on 11 March 2010, but this appears to be due to frustration as being able to move PHP’s development forward. The PHP 5.4 code branch is no longer there. There is however an official PHP 5.4 todo wiki, with Stanislav Malyshev as the tentative release manager. So it looks there will be PHP 5.4, which would push out the PHP 6.0 release further. UPDATE on 24 July 2011: The PHP 5.4 Alpha has been released, and it includes some features originally targeted for PHP 6.0, such as traits and the removal of register_globals and safe_mode.