/**
* Create a new Vertex
*
* @param Graph $graph graph to be added to
* @param string|int $id identifier used to uniquely identify this vertex in the graph
* @see Graph::createVertex() to create new vertices
*/
public function __construct(Graph $graph, $id)
{
if (!is_int($id) && !is_string($id)) {
throw new InvalidArgumentException('Vertex ID has to be of type integer or string');
}
$this->id = $id;
$this->graph = $graph;
$graph->addVertex($this);
}