> And that is especially likely when you use indices manually.
But that is never the recommendation Rust practitioners would give for graph data structures. One would instead recommend using a generational arena, where each index holds their "generation". The arena can be growable or not. When an element is removed from the arena it gets tombstoned, marked as no longer valid. If a new value reuses a tombstoned position, its generation changes. This shifts the cost of verifying the handle is correct at the read point: if the handle corresponds to an index with a tombstone sentinel or has a different generation, the result of the read operation is None, meaning the handle is no longer valid. This is much better than the behavior of pointers.
But that is never the recommendation Rust practitioners would give for graph data structures. One would instead recommend using a generational arena, where each index holds their "generation". The arena can be growable or not. When an element is removed from the arena it gets tombstoned, marked as no longer valid. If a new value reuses a tombstoned position, its generation changes. This shifts the cost of verifying the handle is correct at the read point: if the handle corresponds to an index with a tombstone sentinel or has a different generation, the result of the read operation is None, meaning the handle is no longer valid. This is much better than the behavior of pointers.