The importance of pointer variables in constraint models
Brad Vander Zanden, Brad A. Myers, Dario A. Giuse, Pedro A. Szekely · 1991
Graphical tools are increasingly using constraints to specify the graphical layout and behavior of many parts of an application.However, conventional constraints directly encode the objects they reference, and thus cannot provide support for the dynamic rttntime creation and manipulation of application objects.This paper discusses an extension to current constraint models that allows constraints to indirectly reference objects through pointer variables.Pointer variables permit programmers to create the constraint equivalent of procedures in traditional programming languages.This procedural abstraction allows constraints to model a wide array of dynamic application behavior, simplifies the implementation of structured object and demonstrational systems, and improves the storage and efficiency of highly interactive, graphical applications.It also promotes a simpler, more effective style of programming than conventional constraints.Constraints that use pointer variables are powerful enough to allow a comprehensive user interface toolkit to be built for the first time on top of a constraint system.