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77 lines
2.2 KiB
Rust
77 lines
2.2 KiB
Rust
use std::cell::RefCell;
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use std::mem::ManuallyDrop;
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union U1 {
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a: u8,
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}
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union U2 {
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a: ManuallyDrop<String>,
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}
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union U3<T> {
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a: ManuallyDrop<T>,
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}
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union U4<T: Copy> {
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a: T,
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}
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union URef {
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p: &'static mut i32,
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}
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union URefCell {
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// field that does not drop but is not `Copy`, either
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a: (ManuallyDrop<RefCell<i32>>, i32),
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}
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fn deref_union_field(mut u: URef) {
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// Not an assignment but an access to the union field!
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*(u.p) = 13; //~ ERROR access to union field is unsafe
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}
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fn assign_noncopy_union_field(mut u: URefCell) {
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u.a = (ManuallyDrop::new(RefCell::new(0)), 1); // OK (assignment does not drop)
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u.a.0 = ManuallyDrop::new(RefCell::new(0)); // OK (assignment does not drop)
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u.a.1 = 1; // OK
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}
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fn generic_noncopy<T: Default>() {
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let mut u3 = U3 { a: ManuallyDrop::new(T::default()) };
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u3.a = ManuallyDrop::new(T::default()); // OK (assignment does not drop)
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*u3.a = T::default(); //~ ERROR access to union field is unsafe
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}
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fn generic_copy<T: Copy + Default>() {
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let mut u3 = U3 { a: ManuallyDrop::new(T::default()) };
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u3.a = ManuallyDrop::new(T::default()); // OK
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*u3.a = T::default(); //~ ERROR access to union field is unsafe
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let mut u4 = U4 { a: T::default() };
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u4.a = T::default(); // OK
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}
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fn main() {
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let mut u1 = U1 { a: 10 }; // OK
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let a = u1.a; //~ ERROR access to union field is unsafe
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u1.a = 11; // OK
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let U1 { a } = u1; //~ ERROR access to union field is unsafe
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if let U1 { a: 12 } = u1 {} //~ ERROR access to union field is unsafe
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if let Some(U1 { a: 13 }) = Some(u1) {} //~ ERROR access to union field is unsafe
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// let U1 { .. } = u1; // OK
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let mut u2 = U2 { a: ManuallyDrop::new(String::from("old")) }; // OK
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u2.a = ManuallyDrop::new(String::from("new")); // OK (assignment does not drop)
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*u2.a = String::from("new"); //~ ERROR access to union field is unsafe
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let mut u3 = U3 { a: ManuallyDrop::new(0) }; // OK
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u3.a = ManuallyDrop::new(1); // OK
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*u3.a = 1; //~ ERROR access to union field is unsafe
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let mut u3 = U3 { a: ManuallyDrop::new(String::from("old")) }; // OK
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u3.a = ManuallyDrop::new(String::from("new")); // OK (assignment does not drop)
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*u3.a = String::from("new"); //~ ERROR access to union field is unsafe
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}
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