[hvenev]

I'm struggling to understand how this has anything to do with borrow checking. Borrow checking is a way to reason about aliasing, which doesn't seem to be a concern here.

This post is about memory management and doesn't seem to be concerned much about safety in any way. In C3, does anything prevent me from doing this:

  fn int* example(int input)
  {
      @pool()
      {
          int* temp_variable = mem::tnew(int);
          *temp_variable = input;
          return temp_variable;
      };
  }

[cayley_graph]

Yes, this has little to nothing to do with borrow checking or memory/concurrency safety in the sense of Rust. Uncharitably, the author appears not to have a solid technical grasp of what they're writing about, and I'm not sure what this says about the rest of the language.

[lerno]

No, that is quite possible. You will not be able to use that memory you just returned though. What actually happens is an implementation issue, but it ranges from having the memory overwritten (but still being writable) on platforms with the least support, to being neither read or writable, to throwing an exact error with ASAN on. Crashing on every use is often a good sign that there is a bug.

[unscaled]

It might not be on every use though. The assignment could very well be conditional. If a dangling reference could escape from the arena in which it was allocated, you cannot claim to have memory safety. You can claim that the arena prevents memory leaks (if you remember to allocate everything correctly within the arena), but it doesn't provide memory safety.