Rust proposes new traits for immobile types and guaranteed destructors

Addressing Core Type Assumptions

The Rust project is proposing to introduce new traits that explicitly describe operations possible on a type. Currently, Rust assumes all types can be moved (relocated in memory) and forgotten (via `mem::forget` without running destructors). The new traits, `Move`, `Destruct`, and `Forget`, will allow types to opt out of these default capabilities.

Solving Immobile Types and Self-Referential Data

Many asynchronous futures require self-referential structures, but these types cannot be safely moved. The existing `Pin` mechanism encodes immovability as a property of memory locations rather than types, leading to complexity. The proposed `Move` trait will encode movability as a type property, simplifying the handling of self-referential types, particularly in systems like the Linux kernel.

Ensuring Guaranteed Destructors

Some types, such as `Transaction` or scoped task handles, require their destructors to execute to perform necessary cleanup or finalization. Rust's `mem::forget` function, which prevents destructors from running, is currently safe. This prevents guarantees for destructor execution. The new `Destruct` and `Forget` traits will enable types to ensure their destructors always run, supporting patterns like safe scoped spawns for asynchronous operations.

Precedent and Implementation

This proposal follows the precedent set by the `Sized` hierarchy work, which relaxed the assumption that all types have a compile-time-known size. The project plans to implement Minimum Viable Products (MVPs) in the compiler, write RFCs, and validate the viability through real-world testing, including integration with the Linux Kernel.