> I know nothing about Rust. But why is unsafe needed?
The short of it is that for fundamental computer science reasons the ability to always reject unsafe programs comes at the cost of sometimes being unable to verify that an actually-safe program is safe. You can deal with this either by accepting this tradeoff as it is and accepting that some actually-safe programs will be impossible to write, or you can add an escape hatch that the compiler is unable to check but allows you to write those unverifiable programs. Rust chose the latter approach.
> Kinda sounds a lock would make this safe?
There was a lock, but it looks like it didn't cover everything it needed to.
alt Hacker News
> I know nothing about Rust. But why is unsafe needed?
The short of it is that for fundamental computer science reasons the ability to always reject unsafe programs comes at the cost of sometimes being unable to verify that an actually-safe program is safe. You can deal with this either by accepting this tradeoff as it is and accepting that some actually-safe programs will be impossible to write, or you can add an escape hatch that the compiler is unable to check but allows you to write those unverifiable programs. Rust chose the latter approach.
> Kinda sounds a lock would make this safe?
There was a lock, but it looks like it didn't cover everything it needed to.