Rust's Vec::drain: Leveraging Drop for Safety

This article delves into Rust's Vec::drain method and its Drop implementation, showcasing how ownership prevents subtle bugs—memory-related and otherwise. Vec::drain optimizes performance by maintaining a mutable reference to the original vector and only reading/updating the original storage. The key lies in the Drain struct's Drop implementation, which uses a DropGuard to ensure that even if the iterator is dropped prematurely, remaining elements are safely moved back into the original vector, guaranteeing memory safety. The article thoroughly explains the implementation details of Drain and DropGuard, addressing special cases like zero-sized types and pointer provenance.