/// Takes a collection of collections and pads them with the given element such that all collections are of same length.
/// Returns the new length. Mutates the collections.
#[macro_export]
macro_rules! pad_collection {
    ( $coll:expr, $pad:expr ) => {{
        if $coll.len() > 0 {
            // Find maximum length of a collection
            let mut max_length = $coll[0].len();
            for i in 1..$coll.len() {
                if max_length < $coll[i].len() {
                    max_length = $coll[i].len();
                }
            }
            for i in 0..$coll.len() {
                let l = $coll[i].len();
                if l < max_length {
                    // append might not unroll and hence perform slower
                    //$coll[i].append(&mut vec![$pad; max_length - l]);
                    for _ in 0..max_length - l {
                        $coll[i].push($pad);
                    }
                }
            }

            max_length
        } else {
            0
        }
    }};
}