The type of the parameter passed to the callback, reporting the value of the very important object. The default value is const vipobj_type &, and may be changed if vipobj_type can be type-converted to another class.

A bool value. Setting this parameter to true catches any x::exceptions thrown by a callback lambda, which get logged. The default value of false does not catch any exceptions, which propagate. Note that this means that a thrown exception prevents any additional callbacks from getting invoked, as a result of a very important object update.

The final template parameter specifies the type of the internal mutexes.