An aggregator is a function which follows the following prototype: void (ResultType) where in ResultType is defined as the type which a handler in a dispatcher returns. In the case of a dispatcher of type boost::dispatch::dispatcher<int (int), std::string>, an aggregator must follow the following prototype: void (int).

To be most exact, the Aggregator can safely be a boost::function<void(int)> instance.

The aggregator is called/invoked for every invocation of a handler using the Invoker.