78 lines
1.9 KiB
Rust
78 lines
1.9 KiB
Rust
use std::cell::{RefCell, Ref, RefMut};
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fn main() {
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basic();
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ref_protector();
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ref_mut_protector();
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rust_issue_68303();
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}
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fn basic() {
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let c = RefCell::new(42);
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{
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let s1 = c.borrow();
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let _x: i32 = *s1;
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let s2 = c.borrow();
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let _x: i32 = *s1;
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let _y: i32 = *s2;
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let _x: i32 = *s1;
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let _y: i32 = *s2;
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}
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{
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let mut m = c.borrow_mut();
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let _z: i32 = *m;
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{
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let s: &i32 = &*m;
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let _x = *s;
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}
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*m = 23;
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let _z: i32 = *m;
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}
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{
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let s1 = c.borrow();
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let _x: i32 = *s1;
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let s2 = c.borrow();
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let _x: i32 = *s1;
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let _y: i32 = *s2;
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let _x: i32 = *s1;
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let _y: i32 = *s2;
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}
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}
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// Adding a Stacked Borrows protector for `Ref` would break this
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fn ref_protector() {
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fn break_it(rc: &RefCell<i32>, r: Ref<'_, i32>) {
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// `r` has a shared reference, it is passed in as argument and hence
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// a protector is added that marks this memory as read-only for the entire
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// duration of this function.
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drop(r);
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// *oops* here we can mutate that memory.
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*rc.borrow_mut() = 2;
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}
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let rc = RefCell::new(0);
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break_it(&rc, rc.borrow())
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}
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fn ref_mut_protector() {
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fn break_it(rc: &RefCell<i32>, r: RefMut<'_, i32>) {
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// `r` has a shared reference, it is passed in as argument and hence
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// a protector is added that marks this memory as inaccessible for the entire
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// duration of this function
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drop(r);
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// *oops* here we can mutate that memory.
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*rc.borrow_mut() = 2;
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}
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let rc = RefCell::new(0);
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break_it(&rc, rc.borrow_mut())
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}
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/// Make sure we do not have bad enum layout optimizations.
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fn rust_issue_68303() {
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let optional=Some(RefCell::new(false));
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let mut handle=optional.as_ref().unwrap().borrow_mut();
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assert!(optional.is_some());
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*handle=true;
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}
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