Evolution of dynamic feature usage in PHP

PHP includes a number of dynamic features that, if used, make it challenging for both programmers and tools to reason about programs. In this paper we examine how usage of these features has changed over time, looking at usage trends for three categories of dynamic features across the release histories of two popular open-source PHP systems, WordPress and MediaWiki. Our initial results suggest that, while features such as eval are being removed over time, more constrained dynamic features such as variable properties are becoming more common. We believe the results of this analysis provide useful insights for researchers and tool developers into the evolving use of dynamic features in real PHP programs.