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#![allow(deprecated, invalid_value, clippy::uninit_assumed_init)]
#![warn(clippy::mem_replace_with_uninit)]
use std::mem;
fn might_panic<X>(x: X) -> X {
// in practice this would be a possibly-panicky operation
x
}
fn main() {
let mut v = vec![0i32; 4];
// the following is UB if `might_panic` panics
unsafe {
let taken_v = mem::replace(&mut v, mem::uninitialized());
let new_v = might_panic(taken_v);
std::mem::forget(mem::replace(&mut v, new_v));
}
unsafe {
let taken_v = mem::replace(&mut v, mem::MaybeUninit::uninit().assume_init());
let new_v = might_panic(taken_v);
std::mem::forget(mem::replace(&mut v, new_v));
}
unsafe {
let taken_v = mem::replace(&mut v, mem::zeroed());
let new_v = might_panic(taken_v);
std::mem::forget(mem::replace(&mut v, new_v));
}
// this is silly but OK, because usize is a primitive type
let mut u: usize = 42;
let uref = &mut u;
let taken_u = unsafe { mem::replace(uref, mem::zeroed()) };
*uref = taken_u + 1;
// this is still not OK, because uninit
let taken_u = unsafe { mem::replace(uref, mem::uninitialized()) };
*uref = taken_u + 1;
}
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