Purely functional (persistent) data structures which are natural in GC-d functional languages are a research grade topic in C++/Rust. (Edit: AFAIK: It is due to

Purely functional (persistent) data structures which are natural in GC-d functional languages are a research grade topic in C++/Rust. (Edit: AFAIK: It is due to the additional ownership management/bookkeeping required if there are concurrent access and modification.)