Are PHP applications ready for Hack?

Abstract

Abstract-PHP is by far the most popular WEB scripting language, accounting for more than 80% of existing websites. PHP is dynamically typed, which means that variables take on the type of the objects that they are assigned, and may change type as execution proceeds. While some type changes are likely not harmful, others involving function calls and global variables may be more difficult to understand and the source of many bugs. Hack, a new PHP variant endorsed by Facebook, attempts to address this problem by adding static typing to PHP variables, which limits them to a single consistent type throughout execution. This paper defines an empirical taxonomy of PHP type changes along three dimensions: the complexity or burden imposed to understand the type change; whether or not the change is potentially harmful; and the actual types changed. We apply static and dynamic analyses to three widely used WEB applications coded in PHP (WordPress, Drupal and phpBB) to investigate (1) to what extent developers really use dynamic typing, (2) what kinds of type changes are actually encountered; and (3) how difficult it might be to refactor the code to avoid type changes, and thus meet the constraints of Hack's static typing.We report evidence that dynamic typing is actually a relatively uncommon practice in production PHP programs, and that most dynamic type changes are simple representational changes, such as between strings and integers. We observe that most PHP type changes in these programs are relatively simple, and that the largest proportion of them are easy to refactor to consistent static typing using simple local renaming transformations. Overall, the paper casts doubt on the usefulness of dynamic typing in PHP, and indicates that for many production applications, conversion to Hack's static typing may not be very difficult.

Evolution of PHP Applications: A Systematic Literature Review

“…The steady fashion in which the sampled PHP applications presented in this review have matured, through the use of third party libraries, having dynamic features presented by Hills & Klint, are an indication PHP has the potential to become one of the biggest programming languages, aside it already dominating the web with over 80% of web applications being powered by PHP [4].…”

“…Hack, a new PHP variant endorsed by Facebook, attempts to address this problem by adding static typing to PHP variables, which limits them to a single consistent type throughout execution. [4] 2…”

A User-Oriented Language for Specifying Interconnections Between Heterogeneous Objects in the Internet of Things

“…PHP has a lot to resources because it is a GPL which was designed and is maintained for web applications. Furthermore, PHP is the most popular web scripting GPL [39] for years [38] and it is used in several famous webs. Besides, in last years, Facebook has done a lot of effort in improving this GPL.…”

“…First of all, with the optimisation of HipHop to translate PHP code to C++ code [40]. Secondly, creating a new GPL called Hack, which is a variant of PHP [39], [41], to solve the dynamic typing. Finally, with the HHVM virtual machine that can execute PHP and Hack code.…”

Type unsoundness in practice: an empirical study of Dart

“…An early example is the evaluation of defect-detection capabilities of inter-module type checking in C by Prechelt and Tichy [24]. Souza and Figueiredo [29] have studied Groovy projects to investigate how programmers use optional typing, and Eshkevari et al [10] have evaluated the design of Hack's type system by analyzing the types that occur in PHP programs.…”