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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




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.


Interesting, thanks for sharing!


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




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