Many useful programming language extensions and system support libraries require knowledge of the locations of fields within objects at run time. Examples include orthogonal persistent object stores, precise garbage collectors, data structure picklers, and parameter marshaling schemes. For clean and efficient implementation as libraries, these systems require run-time knowledge of in-memory layouts of data objects, which is unavailable in most traditionally compiled and linked programming languages, such as C, C++, and Ada. Even the recently standardized run-time type identification (RTTI) feature in C++ is insufficient, because it describes only language-level features of the type hierarchy and not the compiler-dependent object layout decisions. We present a facility for run-time type description, or RTTD, which extracts low-level layout information from debugging information generated by conventional compilers, and makes it available to user programs. We believe this to be the simple...