A dimensions aware evaluator for High Energy Physics applications

The LHCb software stack is developed in C++ and uses the Gaudi framework for event processing and DD4hep for the detector description. Numerical computations are done either directly in the C++ code or by an evaluator used to process the expressions embedded in the XML describing the detector geometry. The current system relies on conventions for the physical units used (identical as what is used in the Geant4 simulation framework) and it is up to the developers to ensure that the correct factors are applied to the values entered. Physical units are not primary entities in the framework, it is therefore not possible to check the dimensional consistency of the computation performed. In this paper we investigate the possibilities to add physical units and dimensions to the existing evaluator or to replace it by a more suitable system, and how this would integrate with the possible tools to express units in C++ code (such as boost::units).