exowos/subject_text/vec/access.md

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

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

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

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, last_chunk, or 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 and to_vec functions for the median.

/// 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!()
}

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));
}