75 lines
2.1 KiB
Rust
75 lines
2.1 KiB
Rust
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// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// Example taken from RFC 1238 text
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// https://github.com/rust-lang/rfcs/blob/master/text/1238-nonparametric-dropck.md#examples-of-code-that-will-start-to-be-rejected
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// Compare against test/run-pass/issue28498-must-work-ex2.rs
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use std::cell::Cell;
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#[derive(Copy, Clone, Debug)]
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enum Validity { Valid, Invalid }
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use self::Validity::{Valid, Invalid};
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struct Abstract<T> {
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id: u32,
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nbor: Cell<Option<T>>,
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valid: Validity,
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observe: fn(&Cell<Option<T>>) -> (u32, Validity),
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}
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#[derive(Copy, Clone)]
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struct Neighbor<'a>(&'a Abstract<Neighbor<'a>>);
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fn observe(c: &Cell<Option<Neighbor>>) -> (u32, Validity) {
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let r = c.get().unwrap().0;
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(r.id, r.valid)
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}
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impl<'a> Abstract<Neighbor<'a>> {
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fn new(id: u32) -> Self {
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Abstract {
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id: id,
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nbor: Cell::new(None),
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valid: Valid,
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observe: observe
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}
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}
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}
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struct Foo<T> {
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data: Vec<T>,
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}
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impl<T> Drop for Abstract<T> {
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fn drop(&mut self) {
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let (nbor_id, nbor_valid) = (self.observe)(&self.nbor);
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println!("dropping element {} ({:?}), observed neighbor {} ({:?})",
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self.id,
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self.valid,
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nbor_id,
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nbor_valid);
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self.valid = Invalid;
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}
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}
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fn main() {
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let mut foo: Foo<Abstract<Neighbor>> = Foo { data: Vec::new() };
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foo.data.push(Abstract::new(0));
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foo.data.push(Abstract::new(1));
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foo.data[0].nbor.set(Some(Neighbor(&foo.data[1])));
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//~^ ERROR `foo.data` does not live long enough
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foo.data[1].nbor.set(Some(Neighbor(&foo.data[0])));
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//~^ ERROR `foo.data` does not live long enough
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}
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