Function list 

pub fn list<T, K, P>(
    items: impl Fn() -> Vec<T> + 'static,
    key_of: impl Fn(&T) -> K + 'static,
    build_row: impl Fn(ItemSlot<T, K>) -> P + 'static,
) -> List<T, K>
where
    T: Clone + 'static,
    K: Clone + Hash + 'static,
    P: Piece,

Build a recycling list from a reactive items closure, a key function, and a row builder.