::maybe-dangling

ManuallyDrop<T> and MaybeDangling<T> semantics in stable Rust as per https://github.com/rust-lang/rfcs/pull/3336

This crates offers two types, ManuallyDrop<T>, and MaybeDangling<T>, which do not carry aliasing/dereferenceable-ity properties w.r.t. the T they each contain, which means they are allowed to:

1. have some expired value inside of them, such as T = &'expired …,
2. be fed to a function that does not inspect its value (such as ::core::mem::forget()),
3. exhibit well-defined behavior (no UB!).

References

• The RFC that shall eventually and ultimately supersede this very crate: https://github.com/rust-lang/rfcs/pull/3336

• The miri PR implementing the check against this: https://github.com/rust-lang/miri/pull/2985

• The soundness problem of ::ouroboros stemming from not using this: https://github.com/joshua-maros/ouroboros/issues/88

• The soundness problem of ::yoke stemming from not using this: https://github.com/unicode-org/icu4x/issues/3696

• An URLO thread on the topic, and a post exposing the intention to write this very crate