public <R> Stream<R> invokeAnd(Function<C, R> invoker) {
			Function<C, InvocationResult<R>> mapper = (callbackInstance) -> invoke(
					callbackInstance, () -> invoker.apply(callbackInstance));
			return this.callbackInstances.stream().map(mapper)
					.filter(InvocationResult::hasResult).map(InvocationResult::get);
		}
public < R > Stream < R > invokeAnd ( Function < C , R > invoker ) { Function < C , InvocationResult < R > > mapper = ( callbackInstance ) -> invoke ( callbackInstance , ( ) -> invoker . apply ( callbackInstance ) ) ; return this . callbackInstances . stream ( ) . map ( mapper ) . filter ( InvocationResult :: hasResult ) . map ( InvocationResult :: get ) ; }
Invoke the callback instances where the callback method returns a result.
@param invoker the invoker used to invoke the callback
@param <R> the result type
@return the results of the invocation (may be an empty stream if no callbacks
could be called)