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You can still introduce them via circular strong reference-counted pointers. The solution of course is to have only one strong reference and many weak ones, but the compiler in principle will let you create a cycle that will never get deallocated.

That's the common case, but you can still make a reference counting cycle, or have a thread hang while holding onto something, or even just call `mem::forget` on an allocation.

This is different from Rust's guarantees about memory and thread safety, which you can't break without `unsafe`.

They are, and in a typical program you don't need to worry about leaking memory.

However, it is possible to leak, e.g. if you use a reference-counted type and create a cycle. There's also Box::leak() that does what it says (it's useful for singleton-like things).