All memory-safe languages are built on an unsafe foundation. The Java HotSpot VM is very unsafe C++. That's just how computers work.

You aren't meaningfully sacrificing memory safety by using Rust because the unsafe sections are clearly marked out. That's similar to unsafe C#, Python with ctypes, and many other memory-safe languages.

No, it doesn't. What's interesting isn't so much that random HN posters believe this sort of thing, because hey, who needs to know anything about a topic to post their opinion on a forum right? No, what's fascinating is that this applies to people like Herb Sutter in his "cpp2" language, here's Herb:

> I don’t like monolithic "unsafe" that turns off checking for all rules

Nobody does that. It's possible Herb knows that and is being deceitful but honestly I think it's more likely that without investigating at all Herb has just decided everybody else is an idiot...

    fn trust_me_i_dont_need_a_borrow_checker<'a, 'b> (x: &'a mut u32) -> &'b mut u32 {
        unsafe { core::mem::transmute(x) }
    }

    fn main() {
        let mut owned = vec![40, 2];

        let mut_1 = trust_me_i_dont_need_a_borrow_checker(&mut owned[0]);
        let mut_2 = trust_me_i_dont_need_a_borrow_checker(&mut owned[1]);

        drop(owned);

        let undefined = *mut_1 + *mut_2;
        println!("The answer is {undefined}");
    }

The exact same code, without the transmute (just returning x directly from an unsafe block), fails a type check related to borrowing. Specifically, the compiler can't see why (without a transmute) it should believe that the reference x now has a different lifetime 'b instead of 'a. Which is fair because it doesn't.

The transmute is you claiming it does, and since transmute is an unsafe function that's entirely on you to make sure you're right about that. So, lying has the expected effect.

The borrow checks aren't magic, they can't look into your soul - but they are running inside unsafe code too.

* Edited to make explicit that the alternative is still marked unsafe and yet doesn't work