PHP6 abandoned, going straight to PHP7
In 2005, work began on a project headed by Andrei Zmievski to bring native Unicode support to the language by embedding the International Components for Unicode (ICU) library and internally representing strings as UTF-16. Because this project would lead to major internal and user-affecting changes, it was planned to be the next major PHP version (i.e. version 6) along with a few other features.
By using UTF-16 as default encoding, developers would need to convert the code and all input (e.g. data from requests, database, etc.) from one encoding to UTF-16 and back again. This conversion takes a lot of CPU time, memory (to store the much larger strings), and creates a higher complexity in the implementation due to the increased need to detect the proper encoding for the situation. In light of all of this and the relatively small gain, many contributors became unwilling to use "trunk" as their main development branch and instead either using the stable 5.2/5.3 branches or refusing to do development at all. This shortage of developers led to delays in the project.
In 2009, PHP 5.3 release with many non-Unicode features back-ported from PHP6, most notably namespaces. This became the widely used, stable version of PHP, and in March 2010, the PHP6 project was officially abandoned, and instead PHP 5.4 was prepared containing most remaining non-Unicode features from PHP 6, such as traits and closure re-binding.
Why Jump to PHP7?
After a vote in July of 2014, it was officially decided that the next major release would be called PHP7. The primary reason for even considering the name is the widely-known existence of the previous failed attempt of a new major release, and the existence of numerous books and other resources which already referred to the previous PHP 6. To address potential confusion, there was an RFC (i.e. request for comments) and a vote on whether or not to reuse this name.
Read the rest at the Halls of Valhalla.
By using UTF-16 as default encoding, developers would need to convert the code and all input (e.g. data from requests, database, etc.) from one encoding to UTF-16 and back again. This conversion takes a lot of CPU time, memory (to store the much larger strings), and creates a higher complexity in the implementation due to the increased need to detect the proper encoding for the situation. In light of all of this and the relatively small gain, many contributors became unwilling to use "trunk" as their main development branch and instead either using the stable 5.2/5.3 branches or refusing to do development at all. This shortage of developers led to delays in the project.
In 2009, PHP 5.3 release with many non-Unicode features back-ported from PHP6, most notably namespaces. This became the widely used, stable version of PHP, and in March 2010, the PHP6 project was officially abandoned, and instead PHP 5.4 was prepared containing most remaining non-Unicode features from PHP 6, such as traits and closure re-binding.
Why Jump to PHP7?
After a vote in July of 2014, it was officially decided that the next major release would be called PHP7. The primary reason for even considering the name is the widely-known existence of the previous failed attempt of a new major release, and the existence of numerous books and other resources which already referred to the previous PHP 6. To address potential confusion, there was an RFC (i.e. request for comments) and a vote on whether or not to reuse this name.
Read the rest at the Halls of Valhalla.