object.rs

pub trait Object { }

output.txt

error[E0599]: no method named `wat` found for type `std::boxed::Box<object::Object>` in the current scope
  --> src/stack.rs:57:27
   |
57 |         assert_eq!(canary.wat(), 13);
   |                           ^^^

stack.rs

use object::Object;

pub struct Stack(Vec<Box<Object>>);

impl Stack {
    pub fn new() -> Stack {
        Stack(vec![])
    }

    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }

    pub fn push(&mut self, value: Box<Object>) {
        self.0.push(value);
    }

    pub fn pop(&mut self) -> Box<Object> {
        match self.0.pop() {
            Some(obj) => obj,
            None => panic!("Unable to pop from empty stack!")
        }
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[derive(Debug, PartialEq)]
    struct Canary(usize);
    impl Object for Canary {}
    impl Canary {
        fn wat(&self) -> usize {
            self.0
        }
    }

    #[test]
    fn new() {
        let stack = Stack::new();
        assert!(stack.is_empty());
    }

    #[test]
    fn push() {
        let mut stack = Stack::new();
        stack.push(Box::new(Canary(13)));
        assert!(!stack.is_empty());
    }

    #[test]
    fn pop() {
        let mut stack = Stack::new();
        stack.push(Box::new(Canary(13)));
        let canary = stack.pop();
        assert_eq!(canary.wat(), 13);
    }
}