走进 Rust:引用计数智能指针

Rust About 837 words

概念

单个值可能会有多个所有者。

记录一个值引用的数量来知晓这个值是否仍在被使用。如果某个值有零个引用,就代表没有任何有效引用并可以被清理。

Rc

Rc<T>只能用于单线程场景。

代码

调用Rc::clone加引用计数,调用Rc::strong_count获得强引用的个数。

enum List {
    Cons(i32, Rc<List>),
    Nil,
}

use crate::List::{Cons, Nil};
use std::rc::Rc;

fn main() {
    let a = Rc::new(Cons(5, Rc::new(Cons(10, Rc::new(Nil)))));
    println!("count after creating a = {}", Rc::strong_count(&a));
    let b = Cons(3, Rc::clone(&a));
    println!("count after creating b = {}", Rc::strong_count(&a));
    {
        let c = Cons(4, Rc::clone(&a));
        println!("count after creating c = {}", Rc::strong_count(&a));
    }
    println!("count after c goes out of scope = {}", Rc::strong_count(&a));
}

输出

count after creating a = 1
count after creating b = 2
count after creating c = 3
count after c goes out of scope = 2
Views: 1,006 · Posted: 2023-04-12

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