Function astar 

pub fn astar<G, F, H>(
    graph: &G,
    source: G::Node,
    target: G::Node,
    edge_cost: F,
    estimate_cost: H,
) -> Option<WeightedPath<G::Node>>
where
    G: IndexGraphView,
    F: FnMut(G::Edge) -> u64,
    H: FnMut(G::Node) -> u64,