Comment by sunshowers

> intrusive lists in general

Not quite an intrusive list, but a particular data structure that's often called "intrusive" is a map where keys borrow from values. This turns out to be a super useful pattern.

https://www.boost.org/doc/libs/1_59_0/doc/html/boost/intrusi...

Note that the signature here is `const key_type & operator()(const value_type &)`, or in Rust terms `fn key(&self) -> &Self::Key`. This means that the key must exist in a concrete form inside the value -- it is impossible to have keys that borrow from multiple fields within the value, for example.

At Oxide, I recently wrote and released https://docs.rs/iddqd, which provides similar maps. With iddqd, the signature is `fn key(&self) -> Self::Key<'_>`, which means that iddqd does allow you to borrow from multiple fields to form the key. See the ArtifactKey example under https://docs.rs/iddqd/latest/iddqd/#examples.