The Place trait should be unsafe.

[Stebalien]

Rust will blindly write into whatever pointer is returned by Place::pointer() so the trait itself should be unsafe to implement.

pub unsafe trait Place<Data> where Data: ?Sized {
    fn pointer(&mut self) -> *mut Data;
}

[nagisa]

Alternatively it could return a mutable reference. Any reason it doesn’t, @pnkfelix?

[Stebalien]

Because the returned pointer won't have been initialized (and references should always point to initialized data). We'd need &uninit.

[oli-obk]

another alternative is to return a wrapper type with a lifetime parameter that only has an unsafe constructor (and internally contains the pointer). This type could then offer a safe interface to write into.

[Stebalien]

Closed in favor of an amendment: #1401