Wrong translation for iterator into moved container

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还没有人认领这个 Issue。

评估

难度
5/5
预计耗时
一周以上
新手友好度
15/100
Issue 类型
缺陷
描述清晰度
基本清楚
活跃度
活跃
技术栈
cpp, rust
领域
compilers

调研方向

The issue names no source files or tests, so start by locating how the translator maps C++ std::vector iterators to Rust, which the issue describes as a Value<Vec<T>> wrapper with Weak pointers. Reproduce the moved-container case with the snippet in the issue to confirm the mismatch. Settling the design (the costly Value<Value<Vec<T>>> option or a different invalidation rule) needs maintainer input before any patch.

由索引模型根据 Issue 内容生成。

描述

std::vector<int> src{1, 2, 3};
std::vector<int> dst;

auto it = src.begin();        // (1) iterator to src's first element
dst = std::move(src);         // (2) dst steals src's heap buffer; src is left empty
assert(&*it == &dst[0]);      // (3) C++: true, the element never moved, dst owns it now

let src: Value<Vec<i32>> = Rc::new(RefCell::new(vec![1, 2, 3]));   // Value<T> = Rc<RefCell<T>>
let dst: Value<Vec<i32>> = Rc::new(RefCell::new(Vec::new()));

let it = src.as_pointer().begin();   // (1) Ptr = (Weak to src's Rc, index 0)
dst.write(std::mem::take(&mut *src.borrow_mut()));
                                     // (2) the Vec moves into dst's Rc; src's Rc keeps an empty Vec;
                                     //     `it` still refers to src's Rc
assert!(it.deref() == dst[0]);       // (3) panics: index 0 out of bounds of the empty Vec in src

In C++ the iterator for vector (or other sequential container) stays valid after src is moved because it points into the same buffer. In Rust the iterator is a Weak reference into the src Value<Vec<T>>. It still points into src after the move.

I think the correct solution is to translate vector as Value<Value<Vec<T>> but this is too costly. Also I am not sure if the behavior in C++ is standard behavior or implementation behavior. I found no explicit sentence in the standard that enforces this.

主要语言
Rust
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