A SlotMap has detach/reattach methods, to help with certain access patterns. With the SecondaryMapyou can just use remove/insert for a similar effect.

// &mut self
let x = self.things.remove(id).unwrap();
x.layout(self); // Now I can pass a &mut to things because x is not borrowed
self.things.insert(id, x);

If value removed is small, it doesn't matter, but if the value is bigger it might be nice to have a way to use the same idea, but without moving the object in memory. Would it be possible?

let x = self.things.detach_ref(id); // x is &Thing, or &mut Thing
x.do_stuff(self);
self.things.revive(id);

The slotmap would have to know that one of its values was off limits. Maybe something like this already exists. Maybe that is basically re-inventing RefCell....

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