A Flexible Approach to Interactive Runtime Inspection

Behavioral reflection is well-known approach enabling exhaustive querying of program state (introspection) as well as controlling its execution (intercession). It is hence an adequate foundation for runtime inspection. Partial behavioral reflection aims at making behavioral reflection more applicable by providing high levels of selectivity and configurability. We first outline the main features of partial behavioral reflection and of Reflex—our portable Java implementation. We then sketch how we plan to apply such an approach to provide an interactive environment for runtime inspection, which, in particular, could be used to assist in reflective and aspect-oriented programming. 1 Partial Behavioral Reflection for Java 1.1 Reflection and Behavioral Reflection Reflection in programming languages is a paradigm that has emerged from the studies of Brian Smith around the foundations of consciousness and selfreferences, and his work around the application of these concepts to computer science, down to the implementation of a reflective Lisp dialect [1]. These ideas were then applied to various programming paradigms, including object-oriented programming [2] and had a major impact on languages such as CLOS [3] and Smalltalk [4]. In an object-oriented language, reflection is provided through a MetaObject Protocol (MOP), which is an object-oriented “interface” to the language implementation [3]. The basic property of reflection is to support metacomputations, that is, computations about computations. This is done by separating metacomputations and base computations into two different levels, the metalevel and the base level. These levels are causally connected. This means that, on the one hand, a reflective program running at the base level has access to its representation at the metalevel, and that, on the other hand, a modification of this representation will affect further base computations. Depending on which part of the representation is accessed, the part describing the (static) structure of the program, or the part describing its (dynamic) behavior, reflection is said to be structural or behavioral.