template <typename Func, typename T> struct ContinuationReturnType {
   using type = typename std::invoke_result<Func, T>::type;
};
  
template <typename Func> struct ContinuationReturnType<Func, void> {
   using type = typename std::invoke_result<Func>::type;
};
  
  
template <typename Func, typename T> struct ContinuationFutureType {
   using type = Future<typename RemoveFuture<
       typename ContinuationReturnType<Func, T>::type>::type>;
};
  
template <typename Func, typename T>
using ContinuationFutureType_t = typename ContinuationFutureType<Func, T>::type;
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FROM 27.208.36.*