This has been discussed before. It's the distinction between the collector being precise and conservative. Conservative collectors are fine because they err on

This has been discussed before. It's the distinction between the collector being precise and conservative. Conservative collectors are fine because they err on the side of retaining memory rather than freeing it. As I stated before, intuitively the odds of an integer containing a pointer-like value is 1/4 (on a 32 bit machine), but they actually tend to be much lower. Even libgc has this issue and it is impossible to resolve in C.