Inter-module communication

Communication between modules is done via the exchange of named objects with the event and object manager. Modules therefore do not depend on specific other modules being available in memory or having been run before, but only on whether the necessary data objects have been stored in the event or the object manager. This allows us to completely specify a module by defining which objects or containers it expects as input from the event and object manager and which objects are produced as output in event and object manager. Any two objects using and producing the same objects should be completely interchangeable in running macros. The names of input and output objects for each module should be set to a default value in the modules constructor. They can be overwritten at any time, allowing the same module to be run on the same event with different tuning parameters producing different output containers. Using special tags in the comment fields of the module data member declaration allows the programmer to identify the names of input and output containers. This will be used to automatically check the availability of the containers needed by the module, check whether a particular chain of modules is likely to be consistent and provide automated module documentation. As a rule of thumb, modules should exit gracefully and with a meaningful error message if one of necessary input objects is not found in the event or object manager.