Comment by KingOfCoders
5 hours ago
I always feel Arc is the admission that the borrow checker with different/overlapping lifetimes is too difficult, despite what many Rust developers - who liberally use Arc - claim.
5 hours ago
I always feel Arc is the admission that the borrow checker with different/overlapping lifetimes is too difficult, despite what many Rust developers - who liberally use Arc - claim.
Lifetime tracking and ownership are very difficult. That's why languages like C and C++ don't do it. It's also why those languages needs tons of extra validation steps and analysis tools to prevent bugs.
Arc is nothing more than reference counting. C++ can do that too, and I'm sure there are C libraries for it. That's not an admission of anything, it's actually solving the problem rather than ignoring it and hoping it doesn't crash your program in fun and unexpected ways.
Using Arc also comes with a performance hit because validation needs to be done at runtime. You can go back to the faster C/C++ style data exchange by wrapping your code in unsafe {} blocks, though, but the risks of memory corruption, concurrent access, and using deallocated memory are on you if you do it, and those are generally the whole reason people pick Rust over C++ in the first place.
It's not that the borrow checker is too difficult, it's that it's too limiting.
The _static_ borrow checker can only check what is _statically_ verifiable, which is but a subset of valid programs. There are few things more frustrating than doing something you know is correct, but that you cannot express in your language.
It's not just difficult, sometimes it's impossible to statically know a lifetime of a value, so you must dynamically track it. Arc is one of such tools.