SCG News

Propagation of Behavioral Variations with Delegation Proxies

Camille Teruel, Erwann Wernli, Stéphane Ducasse, and Oscar Nierstrasz. Propagation of Behavioral Variations with Delegation Proxies. In Shigeru Chiba, Éric Tanter, Erik Ernst, and Robert Hirschfeld (Ed.), Transactions on Aspect-Oriented Software Development XII, Lecture Notes in Computer Science 8989 p. 63-95, Springer Berlin Heidelberg, 2015. Details.


Scoping behavioral variations to dynamic extents is useful to support non-functional concerns that otherwise result in cross-cutting code. Unfortunately, such forms of scoping are difficult to obtain with traditional reflection or aspects. We propose delegation proxies, a dynamic proxy model that supports behavioral intercession through the interception of various interpretation operations. Delegation proxies permit different behavioral variations to be easily composed together. We show how delegation proxies enable behavioral variations that can propagate to dynamic extents. We demonstrate our approach with examples of behavioral variations scoped to dynamic extents that help simplify code related to safety, reliability, and monitoring.

Posted by scg at 14 April 2015, 4:36 pm comment link

Polymorphism in the Spotlight: Studying its Prevalence in Java and Smalltalk

Nevena Milojković, Andrea Caracciolo, Mircea Lungu, Oscar Nierstrasz, David Röthlisberger, and Romain Robbes. Polymorphism in the Spotlight: Studying its Prevalence in Java and Smalltalk. In Proceedings of International Conference on Program Comprehension (ICPC 2015), p. 1—10, 2015. To appear. Details.


Subtype polymorphism is a cornerstone of object-oriented programming. By hiding variability in behavior behind a uniform interface, polymorphism decouples clients from providers and thus enables genericity, modularity and extensi- bility. At the same time, however, it scatters the implementation of the behavior over multiple classes thus potentially hampering program comprehension. The extent to which polymorphism is used in real programs and the impact of polymorphism on program comprehension are not very well understood. We report on a preliminary study of the prevalence of polymorphism in several hundred open source software systems written in Smalltalk, one of the oldest object-oriented programming languages, and in Java, one of the most widespread ones. Although a large portion of the call sites in these systems are polymorphic, a majority have a small number of potential candidates. Smalltalk uses polymorphism to a much greater extent than Java. We discuss how these findings can be used as input for more detailed studies in program comprehension and for better developer support in the IDE.

Posted by scg at 30 March 2015, 12:15 pm comment link

Categorising Test Smells

Maudlin Kummer. Categorising Test Smells. Bachelor’s thesis, University of Bern, March 2015. Details.


The aim of this investigation into test smells was to find out how familiar developers are with test smells, the frequency of test smells and their severity in the industrial world. First of all, a taxonomy of different test smells was created and grouped according to programming principles as a basis for this study. Several interviews were then conducted to find out which test smells to include in the subsequent survey. 20 people with different industrial experience levels participated in this survey. It was hypothesised that test smells are not identified as such and that their names are unknown. The hypothesis was supported by the results of the survey. The results revealed that test smells are not quite well-known despite the fact that some of them occur rather frequently and pose severe problems.

Posted by scg at 23 March 2015, 7:15 pm comment link

Towards Faster Method Search Through Static Ecosystem Analysis

Boris Spasojević, Mircea Lungu, and Oscar Nierstrasz. Towards Faster Method Search Through Static Ecosystem Analysis. In Proceedings of the 2014 European Conference on Software Architecture Workshops, ECSAW ’14 p. 11:1—11:6, ACM, New York, NY, USA, August 2014. Details.


Software developers are often unsure of the exact name of the method they need to use to invoke the desired behavior in a given context. This results in a process of searching for the correct method name in documentation, which can be lengthy and distracting to the developer. We can decrease the method search time by enhancing the documentation of a class with the most frequently used methods. Usage frequency data for methods is gathered by analyzing other projects from the same ecosystem - written in the same language and sharing dependencies. We implemented a proof of concept of the approach for Pharo Smalltalk and Java. In Pharo Smalltalk, methods are commonly searched for using a code browser tool called "Nautilus", and in Java using a web browser displaying HTML based documentation - Javadoc. We developed plugins for both browsers and gathered method usage data from open source projects, in order to increase developer productivity by reducing method search time. A small initial evaluation has been conducted showing promising results in improving developer productivity.

Posted by scg at 13 March 2015, 9:15 pm comment link

Mining the Ecosystem to Improve Type Inference For Dynamically Typed Languages

Boris Spasojević, Mircea Lungu, and Oscar Nierstrasz. Mining the Ecosystem to Improve Type Inference For Dynamically Typed Languages. In Proceedings of the 2014 ACM International Symposium on New Ideas, New Paradigms, and Reflections on Programming and Software, Onward! ’14 p. 133—142, ACM, New York, NY, USA, 2014. Details.


Dynamically typed languages lack information about the types of variables in the source code. Developers care about this information as it supports program comprehension. Ba- sic type inference techniques are helpful, but may yield many false positives or negatives. We propose to mine information from the software ecosys- tem on how frequently given types are inferred unambigu- ously to improve the quality of type inference for a single system. This paper presents an approach to augment existing type inference techniques by supplementing the informa- tion available in the source code of a project with data from other projects written in the same language. For all available projects, we track how often messages are sent to instance variables throughout the source code. Predictions for the type of a variable are made based on the messages sent to it. The evaluation of a proof-of-concept prototype shows that this approach works well for types that are sufficiently popular, like those from the standard librarie, and tends to create false positives for unpopular or domain specific types. The false positives are, in most cases, fairly easily identifiable. Also, the evaluation data shows a substantial increase in the number of correctly inferred types when compared to the non-augmented type inference.

Posted by scg at 13 March 2015, 9:15 pm comment link
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