pub trait HasNeighbors<'a, _Outlives = &'a Self> {
    // FIXME: Name should probably be Neighbors
    type NeighborIterType;
}

// FIXME: Name should probably be Neighbors
pub type NeighborIterType<'a, This> = <This as HasNeighbors<'a>>::NeighborIterType;

// FIXME: Name should probably be Neighbors, like the visit trait this is replacing.
pub trait NeighborsIter: visit::GraphBase + for<'a> HasNeighbors<'a> {
    fn neighbors(&self, a: Self::NodeId) -> NeighborIterType<'_, Self>;
}

impl<'a, N, E, Ty, Ix> HasNeighbors<'a> for Graph<N, E, Ty, Ix>
where
    Ty: EdgeType,
    Ix: IndexType,
{
    type NeighborIterType = Neighbors<'a, E, Ix>;
}

impl<N, E, Ty, Ix> NeighborsIter for Graph<N, E, Ty, Ix>
where
    Ty: EdgeType,
    Ix: IndexType,
{
    fn neighbors(&self, a: NodeIndex<Ix>) -> Neighbors<'_, E, Ix> {
        self.neighbors(a)
    }
}