rust - 从 Arc Mutex 获取向量

Question

所以我有这段代码:

use std::sync::{Arc, Mutex}; 

fn main() {
    
    let array = vec!("test", "work", "please");
    let test = Arc::new(Mutex::new(array));
    
    let getter = test.lock().unwrap();
    println!("{:?}", getter);
    
    for item in getter {
        println!("{}", item);
    }
}

它抛出一个错误说:

error[E0277]: `MutexGuard<'_, Vec<&str>>` is not an iterator
  --> src/main.rs:11:17
   |
11 |     for item in getter {
   |                 ^^^^^^ `MutexGuard<'_, Vec<&str>>` is not an iterator
   |
   = help: the trait `Iterator` is not implemented for `MutexGuard<'_, Vec<&str>>`
   = note: required because of the requirements on the impl of `IntoIterator` for `MutexGuard<'_, Vec<&str>>`

哪个，好吧好吧。但我能够执行 let getter = test.lock().unwrap().len(); 并正确获取长度。那么，为什么它在第二种情况下知道它是一个数组，而在第一种情况下却不知道呢？

Answer 1

getter是 MutexGuard实现Deref<Target = Vec<&str>> .当你调用一个方法时，比如 .len() , 它会自动取消引用到 Vec因为没有 .len() MutexGuard 上的方法. for 不会自动完成同样的操作环形。您可以强制手动取消引用:

for item in &*getter {

或者您可以调用.iter()在它上面自动取消引用它:

for item in getter.iter() {

代码:

use std::sync::{Arc, Mutex};

fn main() {
    let array = vec!["test", "work", "please"];
    let test = Arc::new(Mutex::new(array));

    let getter = test.lock().unwrap();
    println!("{:?}", getter);

    for item in &*getter {
        println!("{}", item);
    }

    for item in getter.iter() {
        println!("{}", item);
    }
}

Playground