Is there any C++ stringstream or C# StringBuffer like class in UE4?

I’d like to dynamically edit strings but I am not sure if I can simply use FString’s operands for doing this efficiently.

I wonder if there is any class similar to C++'s stringstream or C#'s StringBuffer in UE.

I’ve searched a bit but couldn’t find anything about this.

Is there no performance issue when I concatenate multiple FStrings?

// any other way that I can do this efficiently?
FString str = FString("aaa") + FString("bbb") + ...

I think closest to stream in UE4 API FArchive which let you serialize properties to any medium (depending on what archive you use)