---
name = "Accessing values"
file = "src/vec/access.rs"
---

Instead of using the good old C-style bound checking:

```rust
if vec.len() < 1 {
    return None;
} else {
    // compiler still thinks this line can panic
    return vec[0];
}
```

Try to implement these functions using non-panicking methods like [`last`](https://doc.rust-lang.org/std/primitive.slice.html#method.last), [`last_chunk`](https://doc.rust-lang.org/std/primitive.slice.html#method.last_chunk), or [`get`](https://doc.rust-lang.org/std/primitive.slice.html#method.get).

> ## note
> Don't be afraid of the `get` function prototype, look at the examples, they are fairly simple, it's just that `get` can work on multiple types, allowing for slice indexing as well as single element indexing.

> ## note
> You may want to look at the [`sort`](https://doc.rust-lang.org/std/primitive.slice.html#method.sort) and [`to_vec`](https://doc.rust-lang.org/std/primitive.slice.html#method.to_vec) functions for the median.

```prototype
/// Add the last two numbers of the input slice.
///
/// # Return value
/// `None` if the slice is not large enough
/// `Some(result)` if the slice has at least 2 elements
pub fn add_last_two(v: &[f32]) -> Option<f32> {
    unimplemented!()
}

/// Duplicate the top element from the stack if it exist
/// (the stack is represented as a Vec with top == last)
///
/// # Return value
/// `Some(())` if the operation succeeded
/// `None` if not
pub fn dup_top(v: &mut Vec<f32>) -> Option<()> {
    unimplemented!()
}

/// Compute the median of a slice in place (if the slice was sorted, it would be the middle element)
pub fn median(v: &[i32]) -> Option<i32> {
    unimplemented!()
}
```

```example
fn main() {
    assert_eq!(add_last_two(&[]), None);
    assert_eq!(add_last_two(&[10.0]), None);
    assert_eq!(add_last_two(&[1.0, 2.0, 3.0]), Some(5.0));

    let mut stack = vec![1.0];
    assert!(dup_top(&mut stack).is_some());
    assert_eq!(&stack, &[1.0, 1.0]);

    stack.clear();
    assert!(dup_top(&mut stack).is_none());

    assert_eq!(median(&[2, 1, 3]), Some(2));
}
```