A CLOS Protocol for Editor Buffers Robert Strandh University of Bordeaux 351, Cours de la Libération Talence, France
[email protected] ABSTRACT because a data structure with optimal asymptotic worst- Many applications and libraries contain a data structure for case complexity would be considered as having too much storing and editing text. Frequently, this data structure is overhead, both in terms of execution time, and in terms of chosen in a somewhat arbitrary way, without taking into memory requirements. account typical use cases and their consequence to perfor- For a text editor with advanced features such as keyboard mance. In this paper, we present a data structure in the macros, it is crucial to distinguish between two different con- form of a CLOS protocol that addresses these issues. In trol loops: particular, the protocol is divided into an edit protocol and • The innermost loop consists of inserting and deleting an update protocol, designed to be executed at different fre- 1 quencies. The update protocol is based on the concept of individual items in the buffer, and of moving one or time stamps allowing multiple views without any need for more cursors from one position to an adjacent posi- observers or similar techniques for informing the views of tion. changes to the model (i.e., the text buffer). • The outer loop consists of updating the views into the In addition to the protocol definition, we also present two buffer. Each view is typically an interval of less than different implementations of the definition. The main im- a hundred lines of the buffer.