Simple Rust stack using Copy and Clone

stack.rs

#[derive(Debug, Copy, Clone)]
pub struct Thing {
    value: f64,
}

struct Node {
    val: Thing,
    next: Option<Box<Node>>,
}

pub struct Stack {
    top: Option<Box<Node>>,
}

impl Stack {
    pub fn new() -> Stack {
        Stack {
            top: None,
        }
    }

    pub fn push(&mut self, val: Thing) {
        self.top = Some(Box::new(Node {
            val: val,
            next: self.top.take(),
        }))
    }

    pub fn pop(&mut self) {
        match self.top.take() {
            None => return,
            Some(mut node_box) => self.top = (*node_box).next.take(),
        }
    }

    pub fn top(&self) -> &Thing {
        match &self.top {
            &None => panic!(),
            &Some(ref node_box) => &(*node_box).val,
        }
    }
}

fn show(t: &mut Thing) {
    t.value += 2.0;
    println!("show: {:?}", t);
}

fn main() {
    let mut st = Stack{top: None};
    
    let mut y = Thing { value: 5.0 };
    st.push(y);
    
    show(&mut y);

    println!("{:?}", y);
}