Comprehensibility of feature dependency in configurable system using #ifdef

<p>Conditional compilation is often used to implement variability in configurable systems. This technique relies on #ifdefs to delimit feature code. Previous studies have shown that #ifdefs may hinder code comprehensibility. However, they did not explicitly take feature dependencies into account. Feature dependency occurs when different features refer to the same program element, such as a variable. Comprehensibility may be even more affected in the presence of feature dependency, as the developer must reason about different scenarios affecting the same variable.&nbsp;Aim: Our goal is to understand how feature dependency affects the comprehensibility of configurable system source code.&nbsp; Method: We conducted two complementary empirical studies. In Study 1 we carried out an experiment in which 30 developers debugged programs with different types of feature dependency. Each program included a different type of feature dependency: global, intraprocedural or interprocedural. We used an eye-tracking device to record developers' gaze movements while they debugged programs. Study 1, however, has two main limitations. Firstly, its programs contain only one type of feature dependency each, while, in real systems, a same program file usually includes more than one type of feature dependency. Secondly, Study 1 does not compare programs with and without feature dependency. In Study 1 we did not compare pieces of source code with and without feature dependency. To minimize those limitations, in this paper we complement Study 1 by means of Study 2. Forty-six developers responded to a web-based study. They executed tasks in which they had to analyze programs containing #ifdef with and without feature dependency. Each program with feature dependency contained all the three types of features dependency as frequently occurs in real configurable systems. Results: In Study 1, debugging programs with #ifdef and global or interprocedural dependency required more time and higher visual effort than intraprocedural dependency. Study 2, analyzing programs containing #ifdef and feature dependency required more time than programs containing #ifdef but without feature dependency. Conclusion: Our study showed that #ifdefs affect comprehensibility of configurable systems in different degrees depending on the presence of feature dependency or type of feature dependency.</p>