(Author here) The project started by taking the cuckoo filter source code (which happens to be written in C++), and extend it. A lot of code comes from that conversion. Other implementations (Morton, CQF) are also written in C++. I write Java normally, so C++ code is not my strength, but C++ was needed to be able to compare with others. A Rust version would be nice!
If you don't understand how having several times as much code as needed, reproducing features also provided by thoroughly-tested Standard libraries, creates reliability risks, this probably will not be the place you learn it. But you could try.
People promoting "safe" languages that don't support encapsulating powerful semantics in libraries prefer to downplay the risks in not having access to such libraries. Needing to open-code the same features, or rely on less well-encapsulated semantics is a fertile source of real-world bugs.
In the race to reliable systems, access to and use of sound, well-tested, usable libraries multiplies efforts.
Downvoting people because you don't understand their argument is disgraceful. Ask.
