Flatten arbitrarily nested arrays in Rust

flatten_array.rs

/* Required some Rust code to flatten an array of arbitrarily nested arrays of integers into a flat array of
 * integers. e.g. [[1,2,[3]],4] -> [1,2,3,4].
 */

/* Model of an arbitrarily nested array of arrays, since native arrays in Rust won't allow that.
 * It is a generic type so that it supports all native numeric types.
 */
enum ArbitrarilyNestedArray<T> {
    Array(Vec<ArbitrarilyNestedArray<T>>),
    Integer(T)
}

/* This will flatten an array of any type implementing the 'Copy' trait, so all numeric
 * types should be covered
 */
fn flatten<T: Copy>(arr: &ArbitrarilyNestedArray<T>) -> Vec<T> {
    match arr {
        // base case
        &ArbitrarilyNestedArray::Integer(x) => vec!(x),
        // recursive case, flatten each member and concat all of them
        &ArbitrarilyNestedArray::Array(ref v) => {
            let mut flat_v = vec!();
            for a in v {
                let flat_a = flatten(a);
                for e in flat_a {
                    flat_v.push(e);
                }
            }
            flat_v
        }
    }
}

/* Basic tests checking some general cases
 */
#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn empty_array() {
        let empty_arr: ArbitrarilyNestedArray<u64> = ArbitrarilyNestedArray::Array(vec!());
        assert!(flatten(&empty_arr).is_empty());
    }

    #[test]
    fn flat_array() {
        let empty_arr = ArbitrarilyNestedArray::Array(vec!(
            ArbitrarilyNestedArray::Integer(1),
            ArbitrarilyNestedArray::Integer(2),
            ArbitrarilyNestedArray::Integer(3)
        ));
        assert_eq!(flatten(&empty_arr), vec!(1,2,3));
    }

    #[test]
    fn deeply_nested_array() {
        let empty_arr = ArbitrarilyNestedArray::Array(vec!(
            ArbitrarilyNestedArray::Array(vec!(
                ArbitrarilyNestedArray::Integer(1),
                ArbitrarilyNestedArray::Integer(2),
                ArbitrarilyNestedArray::Array(vec!(
                    ArbitrarilyNestedArray::Integer(3),
                    ArbitrarilyNestedArray::Array(vec!())
                )),
            )),
            ArbitrarilyNestedArray::Integer(4),
        ));
        assert_eq!(flatten(&empty_arr), vec!(1,2,3,4));
    }
}