Many applications allow user extensions. Extension interfaces appear in everything from collaborative software development website systems (such as Trac plugins) to word processing software (Open Office’s Universal Network Objects) to version control software (Mercurial’s extensions). Here I compare Emacs with two architectures that support user extensions.
Although most people know Eclipse as a popular open source integrated development environment for Java and C++, Eclipse proper includes almost no functionality. Rather, it is a framework for plug-ins, allowing components that support specific aspects of development—writing Java code, debugging a running program, or using version control software—to communicate easily with each other. Eclipse’s architecture allows programmers with a solid solution to one part of the problem to join their work with others’ in order to produce a unified and full-featured development environment.
As a development environment, Eclipse provides valuable features that Emacs lacks. For example, the Java Development Tools plug-ins provide extensive support for refactoring and code analysis. In comparison, Emacs has only a limited understanding of the semantic structure of the programs it edits, and can’t offer comparable support.
Eclipse’s architecture is nothing if not open-ended, as plug-ins provide nearly all significant functionality. There are no second-class citizens: the popular plug-ins are built on the same interfaces ...