But why?

This is usually the case in languages with immutable strings, because concatenation recreates the string every time. But it is not the case in C++ because std::string maintains a dynamic, growable buffer (and std::ostringstream is very likely to maintain a std::string, or some other contiguous buffer internally anyway), without a need for recreating the whole instance, so how does a stream actually help with many concatenations?

It has much less overhead for repeated concatenations, especially with larger datasets.

std::ostringstream is much more preferable than std::string when doing lots of concatenations

I am not sure why? Streams are good for formatting, but how they help with concatenation?

rejected:

1. using namespace std;
2. std::ostringstream is much more preferable than std::string when doing lots of concatenations
3. no random tests

Clojure Translation added

Clojure translation added

C++ translation added

C++ translation added

I published the translation of this Kata but I cant see it in the list