You can surmise the behavior from the signature of clone in the same way that you can memcpy(), it returns an owned type so it will allocate. If you want to match the signature of memcpy then you don't want the allocation and you can instead call clone_from() which takes a mutable borrow of something you had to allocate.

> piece of memory i provided to it, so i can safely do some pointer math with the return value.

Except pointer math is never going to be safe in C, a particular case might be bugfree but it is not safe. Moreover, nothing in the C language says that the provenance of the output pointer matches the provenance of the input pointer (it could take a reference to a pointer from some other thread while that other thread is freeing that memory). In rust you will pass a pointer and get a pointer back with the same lifetime, then you can safely use the pointer in that lifetime bound: the provenance is part of the signature. So in this case, you are incorrectly assuming things from the C signature while the corresponding rust signature definitively tells you.

So yeah, if you learn more about rust then you will see that in fact it tells you more than the corresponding C signatures.