[joshuamorton]

I mean that's functionally what they do, just more accurately since it isn't read time, but time it was built into a binary since that information is accessible, and because the object cache isn't filesystem like and doesn't have an "atime".

And also you still need to reverse from a cached output foo.o, to every transitive dependency of that, of which there could be thousands. Which can be done but requires invoking the build system to do. So it's not anything like just checking a timestamp on the file.

[CyberDildonics]

Nah, conceptually a file system is already an object cache so you can use the filesystem then like use its atime

[joshuamorton]

I realize you're trolling at this point, but no a filesystem and an object cache aren't conceptually similar, in case anyone else might be confused.

[CyberDildonics]

Nah, like conceptually they are both writing serialized bytes and like indexing them so they can conceptually be found easily and like read back. This is probably why you didn't like explain why they are different.