On: Common Rust Lifetime Misconceptions (2020)

[cwzwarich]

`static is actually the superlifetime of all lifetimes, but & is contravariant in its lifetime parameter (and covariant in its type parameter).

[almost_usual → cwzwarich]

Mind expanding on this? The nomicon describes &’a T where both ‘a’ and ‘T’ are covariant. I thought I had a clear picture but now I’m confused.

https://doc.rust-lang.org/nomicon/subtyping.html#variance

[cwzwarich → almost_usual]

Here is the original GitHub issue on the question:

https://github.com/rust-lang/rust/issues/15699

And an RFC by some people that felt frustrated by this arguably implementation-centric view that kind of lost steam:

https://github.com/rust-lang/rfcs/issues/391

Intuitively, the bottom lifetime should the one that is uninhabited, which would be a lifetime with no extent rather than 'static.

[almost_usual → cwzwarich]

Interesting, thanks for sharing!

[Georgelemental → almost_usual]

`rustc` used to use different terminology than the nomicom, but this is no longer the case: https://github.com/rust-lang/rust/pull/107339

[Georgelemental → cwzwarich]

This is not true anymore: https://github.com/rust-lang/rust/pull/107339