The GNAT Implementation of Controlled Types

This paper discusses the implementation model for supporting Ada 95 controlled types in the GNAT compiler. After reviewing the semantics of controlled types, we outline the associated implementation problems and describe their solution in GNAT. The design addresses the management of controlled operations on various entities, including dynamically allocated objects, transient objects (function results and aggregates), and composite objects containing controlled components. The interaction of the controlled type features with exceptions is also covered. Finally, we discuss alternative implementation approaches and possible enhancements to the current model.