PHP4 is seven years old now (amazing!), and PHP5 has been out for nearly three years. But while v4 has gotten pretty long in the tooth, the massive entrenchment of web apps targeted at PHP4 has prevented anything like rapid uptake for version 5. As many as 80% of PHP hosts were still running 4.x as of June 2007. Web hosts who undertake an upgrade risk breaking thousands of customer applications – not OK. But something’s got to break the cycle, which is preventing developers from taking full advantage of all the chocolaty, O-O goodness in v5.
GoPHP5.org is assembling a list of major open source PHP apps committed to dropping all support for v4 by February 2008 as a way to goad hosts into undertaking the difficult transition. The Drupal, Symfony, and phpMyAdmin teams have already signed on, while the WordPress hackers are eager, but wary of the fallout.