alt Hacker NewsI’m sorry, but I look at this code and I can immediately see the bug? Instead of a rewind mark I personally create a local arena from the outer arena. If any allocations leak to the parent scope I put the code in a local function that takes the parent arena as a parameter. Again, if you’re so inclined you can use Rust or C++ to create smart pointers that catch this at runtime or even compile time, it’s just not a real issue for me at this point, reducing the value of complicated compiler machinery leading to bad build times.
That's right! I made the example in such a way that it is obvious what the bug is, for pedagogical reasons :-). This particular bug is a bit trickier to spot when you have more complex programs, and is something that I have seen in real (large) codebases. Your inner/outer arena sounds exactly like the same thing, though?
Generally, it's best to avoid the rewind trick, IMO, it makes it difficult to create composable programs.