mirror of https://github.com/rust-lang/rust
45 lines
1.2 KiB
Rust
45 lines
1.2 KiB
Rust
// A simple example of an unsound mixing of cyclic structure and Drop.
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//
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// Each `D` has a name and an optional reference to another `D`
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// sibling, but also implements a drop method that prints out its own
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// name as well as the name of its sibling.
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//
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// By setting up a cyclic structure, the drop code cannot possibly
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// work. Therefore this code must be rejected.
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//
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// (As it turns out, essentially any attempt to install a sibling here
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// will be rejected, regardless of whether it forms a cyclic
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// structure or not. This is because the use of the same lifetime
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// `'a` in `&'a D<'a>` cannot be satisfied when `D<'a>` implements
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// `Drop`.)
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use std::cell::Cell;
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struct D<'a> {
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name: String,
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p: Cell<Option<&'a D<'a>>>,
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}
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impl<'a> D<'a> {
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fn new(name: String) -> D<'a> { D { name: name, p: Cell::new(None) } }
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}
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impl<'a> Drop for D<'a> {
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fn drop(&mut self) {
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println!("dropping {} whose sibling is {:?}",
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self.name, self.p.get().map(|d| &d.name));
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}
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}
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fn g() {
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let (d1, d2) = (D::new(format!("d1")), D::new(format!("d2")));
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d1.p.set(Some(&d2));
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//~^ ERROR `d2` does not live long enough
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d2.p.set(Some(&d1));
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//~^ ERROR `d1` does not live long enough
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}
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fn main() {
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g();
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}
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