text: ////////////////////////////////////////////////////////////////////////////////
  /// DISCLAIMER
  ///
  /// Copyright 2018 ArangoDB GmbH, Cologne, Germany
  ///
  /// Licensed under the Apache License, Version 2.0 (the "License");
  /// you may not use this file except in compliance with the License.
  /// You may obtain a copy of the License at
  ///
  ///     http://www.apache.org/licenses/LICENSE-2.0
  ///
  /// Unless required by applicable law or agreed to in writing, software
  /// distributed under the License is distributed on an "AS IS" BASIS,
  /// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  /// See the License for the specific language governing permissions and
  /// limitations under the License.
  ///
  /// Copyright holder is ArangoDB GmbH, Cologne, Germany
  ///
  /// @author Simon Grätzer
  ////////////////////////////////////////////////////////////////////////////////
  
  #ifndef ARANGODB_FUTURES_EXCEPTIONS_H
  #define ARANGODB_FUTURES_EXCEPTIONS_H 1
  
  #include <cstdint>
  #include <exception>
  
  namespace arangodb {
  namespace futures {
  
  enum class ErrorCode : uint8_t {
    BrokenPromise = 1,
    FutureAlreadyRetrieved = 2,
    FutureNotReady = 3,
    PromiseAlreadySatisfied = 4,
    NoState = 5
  };
  
  struct FutureException : public std::exception {
    FutureException(ErrorCode code) : _code(code) {}
  
    ErrorCode code() const noexcept { return _code; }
  
    char const* what() const noexcept override {
      switch (_code) {
        case ErrorCode::BrokenPromise:
          return "Promise abandoned the shared state";
        case ErrorCode::FutureAlreadyRetrieved:
          return "Future was already retrieved";
        case ErrorCode::FutureNotReady:
          return "Future is not ready";
        case ErrorCode::PromiseAlreadySatisfied:
          return "Promise was already satisfied";
        case ErrorCode::NoState:
          return "No shared state";
        default:
          return "invalid future exception";
      }
    }
  
   private:
    ErrorCode _code;
  };
  
  }  // namespace futures
  }  // namespace arangodb
  
  #endif
  