message: Fixed the compilation errors in older standard versions, which latest draft compiles successfully.
diff: @@ -136,7 +136,7 @@ private:
  //TODO: shall we handle overflow cases like
  // oatpp::String json = "128";
  // auto value = jsonObjectMapper->readFromString<oatpp::Int8>(json); // UInt8 will overflow to -128
  - return T(static_cast<T::UnderlyingType>(caret.parseInt()));
  + return T(static_cast<typename T::UnderlyingType>(caret.parseInt()));
  }
  }
  @@ -153,7 +153,7 @@ private:
  //TODO: shall we handle overflow cases like
  // oatpp::String json = "256";
  // auto value = jsonObjectMapper->readFromString<oatpp::UInt8>(json); // UInt8 will overflow to 0
  - return T(static_cast<T::UnderlyingType>(caret.parseUnsignedInt()));
  + return T(static_cast<typename T::UnderlyingType>(caret.parseUnsignedInt()));
  }
  }
  