typically, if you're operating upon a particular comment, you've gotten there by traversing to it from the parent. Ensuring that traversals don't encounter cy

typically, if you're operating upon a particular comment, you've gotten there by traversing to it from the parent. Ensuring that traversals don't encounter cycles is easy, keep hold of a hashtable (or a set) of comment ids as you traverse. As the traversal encounters a comment, its id is added to the hash, and as you complete traversal of each comment, the id is removed. If you encounter an id that's already in the set, assertion failed - or better yet, log the condition and then cease the traversal. That way everything keeps running and the error is visible in the logs. If the code is organized (as it should be) such that all functions which require traversal of hierarchical comments pull this from a single function, then the hash check only need be applied in that one place in the code, where it need not be visible anywhere else.