rust--Deref/DerefMut

用CustomSmartPointer包装了一下，相当直接调用String的方法

struct CustomSmartPointer<T>(T);

impl<T> CustomSmartPointer<T> {
    fn new(x: T) -> CustomSmartPointer<T> {
        CustomSmartPointer(x)
    }
}
impl<T> Deref for CustomSmartPointer<T> {
    type Target = T;

    fn deref(&self) -> &T {
        &self.0
    }
}
#[test]
fn test02() {
    let xx = CustomSmartPointer::new(String::from("xxxxx"));
    println!("{}", xx.len());
}