Question

I wanna create and store graph in php. I have bus schedule, so I decided to create 2 classes:

class Vertex 
{
  public $city_id;
  public $time;
}

class Edge
{
  public routeId;
  public end_vertex;
}

after this I’m trying to fill my graph. It should be something like hashtable where key will be Vertex object and it’ll have many edges.

prototype example:

foreach ($data as $route)
{
  $v = new Vertex($route->startCity, $route->startTime)
  if(!graph[$v]) {
    graph[$v] = [];
  }

  graph[$v].add(new Edge($route->routeId, new Vertex($route->city_id, $route->startTime + $route->arrivalTime)));
}

but there is one really big problem, as I understand object cannot be used as array key! Maybe I’m in a wrong way? How to create graphs correctly in php? I’m a newbie in this.

Answer 1

In PHP, only simple types can be used as array indices. Complex types, like arrays, objects and resources do not work properly.

Edit: Oh, if memory serves me right, you should watch out for booleans as well, I seem to recollect an issue I had with them.

Edit2: In your case, the object graph should be pointing at the objects, not an array.

So, for example, your code would look like:

$v = new Vertex();

$v->add(new Edge());

$vertices[] = $v;

Edit3: I noticed some serious syntactic flaws in your code. I don’t know the exact reason, but if you really can’t get them straight, I would advice that you give the PHP manual a couple of looks.

Edit4: By the way, you are using an object as an array index, not a class. There is no PHP data type for classes, there is only class names, which are plain strings.