public static IAsyncResult BeginSchedule(this IActionScheduler actionScheduler,
int estimateCost,
Func <IAsyncResult> begin,
Action <IAsyncResult> end,
Func <int> actualCost = null, Func <Exception, int> exceptionCost = null)
=> actionScheduler.BeginSchedule(estimateCost, begin, ia => { end(ia); return(0); }, actualCost == null ? default(Func <int, int>) : _ => actualCost(), exceptionCost);
