In his latest post, John Lim looks at some of the issues that he (and his group of developers) are having in the port from legacy PHP4 applications up to PHP 5.1.

Today, started to test moving some of our PHP4 apps to PHP5.1.1. Some of this code was written for PHP 4.0.6, over 3 years ago. The migration so far has been relatively painless. Here are some of the problems we encountered.

Included in his list are things like:

• issues with code generators (created in PHP4) and pass by reference problems
• the classic register_globals issues
• the lack of an open source opcode cache for Windows
• and more...