Variable Feature Usage Patterns in PHP

PHP allows the names of variables, classes, functions, methods, and properties to be given dynamically, as expressions that, when evaluated, return an identifier as a string. While this provides greater flexibility for programmers, it also makes PHP programs harder to precisely analyze and understand. In this paper we present a number of patterns designed to recognize idiomatic uses of these features that can be statically resolved to a precise set of possible names. We then evaluate these patterns across a corpus of 20 open-source systems totaling more than 3.7 million lines of PHP, showing how often these patterns occur in actual PHP code, demonstrating their effectiveness at statically determining the names that can be used at runtime, and exploring anti-patterns that indicate when the identifier computation is truly dynamic.