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Comment by sorokod | Hacker News Reader

About cached values you say: "Synchronizing" them is always as simple as a single, controlled operation.

Others have stated that: "There are only two hard things in Computer Science: cache invalidation and naming things"

I don't think that's what he's arguing though—it's not a cache like memcached or anything, it's much more abstract than that. He's saying that calculating values derived from the program state should be as simple as possible, and not have other side effects.

Caching comes with a bunch of strings attached of which recalculating the values is the least problematic.

I think the name “cached value” is a red herring, as far as the mindset being described is considered. “Derived value” might be closer to the mark; the values are pure functions of other things, and to change the derived value you must change the things it depends on. There need not be any mention of storing that derived value in a cache and somehow invalidating it.

I've always heard it as

"There are two hard problems in Computer Science: cache invalidation, naming things, and off-by-one errors"

Yes :) This does not solve the problem of cache invalidation, it only separates it from other concerns so that it can be focused on explicitly.

"Cached values" isn't a great name here. He should probably call them "Derived values".

The word "cache" was used to encompass remote values too; i.e. ones that an external system may derive from its own state, but where that component is behind a black box.

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