It doesn't though.

Those are fairly straightforward to implement if you are ok using a reference counted type (along with weak references), although that will hurt performance. That would be similar to using a shared_pointer in c++.

And you can implement code similar to what you would in c or c++ if you use raw pointers and unsafe code.

Where you run into difficulties is if you want something that is fast and safe. And then you need a more complicated design that probably involves using indices into a Vec instead of pointers.