Variable Feature Usage Patterns in PHP Mark Hills East Carolina University, Greenville, NC, USA
[email protected] Abstract—PHP allows the names of variables, classes, func- and classes at runtime. Below, we refer to these generally as tions, methods, and properties to be given dynamically, as variable features, and specifically as, e.g., variable functions expressions that, when evaluated, return an identifier as a string. or variable methods. While this provides greater flexibility for programmers, it also makes PHP programs harder to precisely analyze and understand. The main contributions presented in this paper are as follows. In this paper we present a number of patterns designed to First, taking advantage of our prior work, we have developed recognize idiomatic uses of these features that can be statically a number of patterns for detecting idiomatic uses of variable resolved to a precise set of possible names. We then evaluate these features in PHP programs and for resolving these uses to a patterns across a corpus of 20 open-source systems totaling more set of possible names. Written using the Rascal programming than 3.7 million lines of PHP, showing how often these patterns occur in actual PHP code, demonstrating their effectiveness at language [2], [3], these patterns work over the ASTs of the statically determining the names that can be used at runtime, PHP scripts, with more advanced patterns also taking advantage and exploring anti-patterns that indicate when the identifier of control flow graphs and lightweight analysis algorithms for computation is truly dynamic. detecting value flow and reachability. Each of these patterns works generally across all variable features, instead of being I.