1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
|
use std::cell::RefCell;
use std::mem::ManuallyDrop;
union U1 {
a: u8,
}
union U2 {
a: ManuallyDrop<String>,
}
union U3<T> {
a: ManuallyDrop<T>,
}
union U4<T: Copy> {
a: T,
}
union URef {
p: &'static mut i32,
}
union URefCell {
// field that does not drop but is not `Copy`, either
a: (ManuallyDrop<RefCell<i32>>, i32),
}
fn deref_union_field(mut u: URef) {
// Not an assignment but an access to the union field!
*(u.p) = 13; //~ ERROR access to union field is unsafe
}
fn assign_noncopy_union_field(mut u: URefCell) {
u.a = (ManuallyDrop::new(RefCell::new(0)), 1); // OK (assignment does not drop)
u.a.0 = ManuallyDrop::new(RefCell::new(0)); // OK (assignment does not drop)
u.a.1 = 1; // OK
}
fn generic_noncopy<T: Default>() {
let mut u3 = U3 { a: ManuallyDrop::new(T::default()) };
u3.a = ManuallyDrop::new(T::default()); // OK (assignment does not drop)
*u3.a = T::default(); //~ ERROR access to union field is unsafe
}
fn generic_copy<T: Copy + Default>() {
let mut u3 = U3 { a: ManuallyDrop::new(T::default()) };
u3.a = ManuallyDrop::new(T::default()); // OK
*u3.a = T::default(); //~ ERROR access to union field is unsafe
let mut u4 = U4 { a: T::default() };
u4.a = T::default(); // OK
}
fn main() {
let mut u1 = U1 { a: 10 }; // OK
let a = u1.a; //~ ERROR access to union field is unsafe
u1.a = 11; // OK
let U1 { a } = u1; //~ ERROR access to union field is unsafe
if let U1 { a: 12 } = u1 {} //~ ERROR access to union field is unsafe
if let Some(U1 { a: 13 }) = Some(u1) {} //~ ERROR access to union field is unsafe
// let U1 { .. } = u1; // OK
let mut u2 = U2 { a: ManuallyDrop::new(String::from("old")) }; // OK
u2.a = ManuallyDrop::new(String::from("new")); // OK (assignment does not drop)
*u2.a = String::from("new"); //~ ERROR access to union field is unsafe
let mut u3 = U3 { a: ManuallyDrop::new(0) }; // OK
u3.a = ManuallyDrop::new(1); // OK
*u3.a = 1; //~ ERROR access to union field is unsafe
let mut u3 = U3 { a: ManuallyDrop::new(String::from("old")) }; // OK
u3.a = ManuallyDrop::new(String::from("new")); // OK (assignment does not drop)
*u3.a = String::from("new"); //~ ERROR access to union field is unsafe
}
|
