Scala fuses object-oriented and functional programming in a statically typed programming language. It is aimed at the construction of components and component systems. This paper gives an overview of the Scala language for readers who are familar with programming methods and programming language design.

We identify three programming language abstractions for the construction of reusable components: abstract type members, explicit selftypes, and modular mixin composition. Together, these abstractions enable us to transform an arbitrary assembly of static program parts with hard references between them into a system of reusable components. The transformation maintains the structure of the original system. We demonstrate this approach in two case studies, a subject/observer framework and a compiler front-end.

Feature-Oriented Software Development (FOSD) provides a multitude of formalisms, methods, languages, and tools for building variable, customizable, and extensible software. Along different lines of research different ideas of what a feature is have been developed. Although the existing approaches have similar goals, their representations and formalizations have not been integrated so far into a common framework. We present a feature algebra as a foundation of FOSD. The algebra captures the key ideas and provides a common ground for current and future research in this field, in which also alternative options can be explored.

We present the programming language Keris, an extension of Java with explicit support for software evolution. Keris introduces extensible modules as the basic building blocks for software. Modules are composed hierarchically revealing explicitly the architecture of systems. A distinct feature of the module design is that modules do not get linked manually. Instead, the wiring of modules gets infered. The module assembly and refinement mechanism of Keris is not restricted to the unanticipated extensibility of atomic modules. It also allows to extend fully linked systems by replacing selected submodules with compatible versions without needing to re-link the full system. Extensibility is type-safe and non-invasive; i.e. the extension of a module preserves the original version and does not require access to source code.

Scala fuses object-oriented and functional programming in a statically typed programming language. It is aimed at the construction of components and component systems. This paper gives an overview of the Scala language for readers who are familar with programming methods and programming language design.

The object-oriented programming language design space consists of class-based and prototype-based languages. Both language families have been shown to posses many advantages but also several disadvantages with respect to software construction. Hybrid languages featuring both prototype-based and class-based mechanisms have been proposed as a solution. Unfortunately these languages not only unify the advantages but also the disadvantages of both families. In this paper we propose a more intersectional point of view and propose a language that inherits the advantages but shuns the disadvantages of both families.

www.iam.unibe.ch/∼scg Although the term software component has become commonplace, there is no universally accepted definition of the term, nor does there exist a common foundation for specifying various kinds of components and their compositions. We propose such a foundation. The Piccola calculus is a process calculus, based on the asynchronous π-calculus, extended with explicit namespaces. The calculus is high-level, rather than minimal, and is consequently convenient for expressing and reasoning about software components, and different styles of composition. We motivate and present the calculus, and outline how it is used to specify the semantics of Piccola, a small composition language. We demonstrate how the calculus can be used to simplify compositions by partial evaluation, and we briefly outline some other applications of the calculus to reasoning about compositional styles.

Each object-oriented programming language proposes various grouping mechanisms to bundle interacting classes (i.e., packages, modules, selector namespaces, etc). To understand this diversity and to compare the different approaches, a common foundation is needed. In this paper we present a simple module calculus consisting of a small set of operators over environments and modules. Using these operators, we are then able to specify a set of module combinators that capture the semantics of Java packages, C# namespaces, Ruby modules, selector namespaces, gbeta classes, classboxes, MZScheme units, and MixJuice modules. We develop a simple taxonomy of module systems, and show how particular combinations of module operators help us to draw sharp distinctions between classes of module systems that share similar characteristics.

We describe support for modularity in Newspeak, a programming language descended from Smalltalk [33] and Self [68]. Like Self, all computation — even an object’s own access to its internal structure — is performed by invoking methods on objects. However, like Smalltalk, Newspeak is class-based. Classes can be nested arbitrarily, as in Beta [44]. Since all names denote method invocations, all classes are virtual; in particular, superclasses are virtual, so all classes act as mixins. Unlike its predecessors, there is no static state in Newspeak, nor is there a global namespace. Modularity in Newspeak is based exclusively on class nesting. There are no separate modularity constructs such as packages. Top level classes act as module definitions, which are independent, immutable, self-contained parametric namespaces. They can be instantiated into modules which may be stateful and mutually recursive.

Software components can be implemented and distributed as collections of classes, then adapted to the needs of specific applications by means of subclassing. Unfortunately, subclassing in collections of related classes may require re-implementation of otherwise valid classes just because they utilize outdated parent classes, a phenomenon that is referred to as the subclassing anomaly. The subclassing anomaly is a serious problem since it can void the benefits of component-based programming altogether. We propose a code adaptation language mechanism called class overriding that is intended to overcome the subclassing anomaly. Class overriding does not create new and isolated derived classes as subclassing does, but rather extends and updates existing classes across collections of related classes. If adopted in new languages for component-based programming, or in existing compiled languages such as C# and Java, class overriding can help maintain the integrity of evolving collections of related classes and thus enhance software component adaptability.