alt Hacker News> The only thing unsafe does is let you have an unbounded lifetime.
No, you're wrong: You can create any lifetime. Proof:
fn oof<'desired>(x: &u32) -> &'desired u32 {
let ptr = x as *const u32;
unsafe { &*ptr }
}
> You don't disable anything.
I said "effectively disable". For example:
fn trust_me_bro<'a>(x: mut u32) -> &'a mut u32 { unsafe { &mut x } }
fn main() {
let mut x = 1_u32;
let reference_a = &mut x;
let reference_b = trust_me_bro(reference_a);
*reference_b = 2; -- Whoops
println!("reference_a: {reference_a} reference_b: {reference_b}");
}
> Proof:
You just listed examples of unbounded lifetimes.
> I said "effectively disable". For example:
Not sure what you meant by this example since it doesn't compile. It seems the borrow checker caught your mischief. So much for effectively disabling stuff :P
You haven't effectively disabled anything; you just (tried to) wrote unsound code that washes one mutable ref as another. This stuff is allowed provided shared refs are never accessed at the same time (for example, panicking upon reading reference_b).
What you probably meant is https://play.rust-lang.org/?version=stable&mode=debug&editio...
But you know what? If you're dabbling in unsafe, you have this big button called Tools in the playground. Choose Miri, then run your code; it will display large Undefined behavior. It even highlights the `trust_me_bro` function.
Hell, run this with UBSAN, ASAN, and other C tools. They will probably catch any such behavior.