rust - 当计数为 1 时，有条件地将 T 从 Rc 移出

Question

有没有办法从 Rc<T> 中移动对象？当计数为 1 时？我正在考虑如何实现:

fn take_ownership<T>(shared: Rc<T>) -> Result<T, Rc<T>> { ... }

语义是你得到 T如果计数是 1然后你回来shared否则，您可以稍后再试。

Answer 1

标准库提供了 Rc::try_unwrap功能:

fn try_unwrap(this: Rc<T>) -> Result<T, Rc<T>>

Returns the contained value, if the Rc has exactly one strong reference.

Otherwise, an Err is returned with the same Rc that was passed in.

This will succeed even if there are outstanding weak references.

Examples

use std::rc::Rc;

let x = Rc::new(3);
assert_eq!(Rc::try_unwrap(x), Ok(3));

let x = Rc::new(4);
let _y = Rc::clone(&x);
assert_eq!(*Rc::try_unwrap(x).unwrap_err(), 4);