use crate::graph::Error;
pub trait Graph<'a, N: 'a> {
type NodeIterator: Iterator<Item=&'a N>;
type NeighborIterator: Iterator<Item=&'a N>;
type EdgeIterator: Iterator<Item=(&'a N, &'a N)>;
fn is_empty(&self) -> bool;
fn order(&self) -> usize;
fn size(&self) -> usize;
fn nodes(&'a self) -> Self::NodeIterator;
fn has_node(&self, node: &N) -> bool;
fn neighbors(&'a self, node: &N) -> Result<Self::NeighborIterator, Error>;
fn degree(&self, node: &N) -> Result<usize, Error>;
fn edges(&'a self) -> Self::EdgeIterator;
fn has_edge(&self, source: &N, target: &N) -> Result<bool, Error>;
}