Box<T>:在heap內(nèi)存上分配值
Rc<T>: 啟用多重所有權(quán)的引用技術(shù)類型
Ref<T>     RefMut<T>     通過(guò)RefCall<T> 訪問(wèn)：在運(yùn)行時(shí)而不是編譯時(shí)強(qiáng)制借用規(guī)則的類型

    let b = Box::new(5);
    println!("b = {}",b);

    let x = 5;
    let y = &x;
    assert_eq!(5,x);
    assert_eq!(5,*y);

    let y = Box::new(5);
    assert_eq!(5,*y);

struct Mypointer<T>(T); //結(jié)構(gòu)體元組，只有一個(gè)成員
//元組結(jié)構(gòu)體相當(dāng)于沒(méi)有成員名字的結(jié)構(gòu)體，通過(guò)索引訪問(wèn)
impl<T> Mypointer<T> {
    fn new(x : T) -> Mypointer<T> {
        Mypointer(x)
    }
}
//要讓其成為指針，需要實(shí)現(xiàn)Deref方法
impl<T> Deref for Mypointer<T> {
    type Target = T;
    fn deref(&self) -> &T {
        &self.0
    }
}
    let y = Mypointer::new(5);
    assert_eq!(5,*y);

fn hello(name :  & str) {
    println!("hello,{}",name);
}
    hello("Rust");
    let m = Mypointer::new(String::from("Rust"));
        //原始類型為 &mypointer<String>
        // deref &string
        // deref &str
    hello(&m);

impl<T> Drop for Mypointer<T> {
    fn drop(&mut self) {
        println!("run drop function----")
    }
}

enum Node2 {
    Next2(i32 ,Rc<Node2> ),
    Nul
}
use self::Node2::Next2;
use self::Node2::Nul;
.... main.....
    let a = Rc::new( Next2(5, Rc::new( Nul ) ));
    println!("a value is {}",Rc::strong_count(&a));
    let b = Rc::new( Next2(
        12, Rc::clone(&a)
        )
    );
    println!("after b :a value is {}",Rc::strong_count(&a));
    let c = Rc::new(
        Next2(  11, Rc::clone(&a)  )
    );
    println!("after c: a value is {}",Rc::strong_count(&a));
    {
        let d = Rc::new(
            Next2(  15, Rc::clone(&a)  )
        );
        println!("after d :a value is {}",Rc::strong_count(&a));
    }
    println!("end : a value is {}",Rc::strong_count(&a));
....end....

let a = 10;
let b = &mut a;//錯(cuò)誤