drop-trait

  1. Drop trait类似于其他语言中的析构函数，值离开作用域的时候执行函数的代码
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struct Dog {
name: String,
        //count: i32,
}

impl Drop for Dog {
  fn drop(&mut self) { //走的时候需要释放Dog，所以是mut
    println!("Dog {} leave",self.name);
    //self.count -= 1;
  }
}

fn main() {
  let a = Dog{name: String::from("wangcai")};
  {let b = Dog{name: String::from("dahuang")};
    println!("0++++++++++++++++++");

  }
  println!("1++++++++++++++++++");

}

//首先释放的是b，然后是a
//0++++++++
//Dog dahuang leave
//1++++++++
//Dog wangcai leave

drop的提前释放

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struct Dog {
    name: String,
  }

impl Drop for Dog {
    fn drop(&mut self) {
        println!("{} leave",self.name);
      }
  }

fn main() {
  let a = Dog{name: String::from("wangcai")};
  let b = Dog{name: String::from("dahuang")};
  //dahuang leave
  //wangcai leave
  //可以看出值在栈上

  //如果提前leave
  
  //报错，drop不允许显式调用，正确写法是
  //b.drop();
  drop(b);
  drop(a);
  
  }