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Comment by kaspermarstal | Hacker News Reader

> Don’t ask me about covariance since I honestly don’t know the answer. I recommend reading the section on subtyping and variance and The Rustonomicon. I went through them a few times but still don’t entirely get all the details. Then, we can define each type of object like so:

Haha this is gold. We ALL do this ALL the time.

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haha, glad to know that I'm not the only one

I get tripped up by variance too and thinking about that stuff is literally my job. If it helps, I wrote a blog post recently about Go's type system and it happens to touch in variance in a way that might help it click:

https://journal.stuffwithstuff.com/2023/10/19/does-go-have-s...

The very first sentence of that article got me excited:

>I’ve been noodling on a static type system for my current hobby language.

As an inveterate language tinkerer for decades, Crafting Interpreters is like the intersection of Class A narcotic addiction, Feynman level understanding and religious enlightenment. It's in my top 3 favourite books of all time.

If you were to /happen/ to write an extension/follow up book that addressed static typing, then I can personally guarantee at least one sale.

Independent of that, thanks for the work as it stands. My copy is healthily dog-eared and still gets lugged around on holidays for refresh reading.

Thanks for sharing. I've enjoyed every single piece of your writing so far. This will be in the arsenal of materials I'll use when I again get confused about variance.

Definitely not the only one. I am not a stupid person*, but every single time I read the section on variance in the Nomicon I feel like an utter moron.

*source: trust me bro

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