I give Rust a lot of points for putting control over covariance into the language without making anyone remember which one is covariance and which one is contravariance.
I give Rust a lot of points for putting control over covariance into the language without making anyone remember which one is covariance and which one is contravariance.
One of the things that makes typing an existing codebase difficult in Python is dealing with variance issues. It turns out people get these wrong all over the place in Python and their code ends up working by accident.
Generally it’s not worth trying to fix this stuff. The type signature is hell to write and ends up being super complex if you get it to work at all. Write a cast or Any, document why it’s probably ok in a comment, and move on with your life. Pick your battles.
Kotlin uses "in" and "out": https://kotlinlang.org/docs/generics.html
Co- means with. Contra- means against. There are lots of words with these prefixes you could use to remember (cooperate, contradict, etc.).