How often do you break your phone that you've save sooo much? Mine is at least 2 years older (I got it 2 years before the Fairphone 4 was released) and I've spend 0$ dollars repairing it.

RAID is not backup, but in some circumstances it's better than a backup. If you don't have RAID and your disk dies you need to replace it ASAP and you've lost all changes since your last backup. If you have RAID you just replace the disk and suffer 0 data loss.

That being said, the reason why I'm afraid of not using RAID is data integrity. What happens when the single HDD/SSD in your system is near its end of life? Can it be trusted to fail cleanly or might it return corrupted data (which then propagates to your backup)? I don't know and I'd be happy to be convinced that it's never an issue nowadays. But I do know that with a btrfs or zfs RAID and the checksuming done by these file systems you don't have to trust the specific consumer-grade disk in some random laptop, but instead can rely on data integrity being ensured by the FS.

I was a bit confused by the remark that comptime is referentially transparent. I'm familiar with the term as it's used in functional programming to mean that an expression can be replaced by its value (stemming from it having no side-effects). However, from a quick search I found an old related comment by you [1] that clarified this for me.

If I understand correctly you're using the term in a different (perhaps more correct/original?) sense where it roughly means that two expressions with the same meaning/denotation can be substituted for each other without changing the meaning/denotation of the surrounding program. This property is broken by macros. A macro in Rust, for instance, can distinguish between `1 + 1` and `2`. The comptime system in Zig in contrast does not break this property as it only allows one to inspect values and not un-evaluated ASTs.

[1]: https://news.ycombinator.com/item?id=36154447

This is honestly really cool! I've heard praises about Zig's comptime without really understanding what makes it tick. It initially sounds like Rust's constant evaluation which is not particularly capable. The ability to have types represented as values at compilation time, and _only_ at compile time, is clearly very powerful. It approximates dynamic languages or run-time reflection without any of the run-time overhead and without opening the Pandora's box that is full blown macros as in Lisp or Rust's procedural macros.

> I'm not very familiar with these relations, but shouldn't function returns be covariant? `String => Cat` is a subtype of `String => Animal`?

You're right :) I mixed up covariance and contravariance for function parameters and return value in my comment.

> For function parameters, doesn't it depend on how the parameter is used?

I don't think so, but maybe there's specific circumstances I don't know of? Function parameter types is a constraint on _input_ to the function. Changing that to a subtype amounts to the function receiving arguments that satisfies a stronger constraint. That seems that something that would hold no matter how the parameter is used?