Finding elements of a given type in an array in C#

Question

I have a Fleet class that contains an array of (base class) Vehicles. The vehicles in the array are subclasses of Vehicles: Plains, Trains and Automobiles. The array is private, but the Fleet class must offer a method to get at the vehicles of a given type.

Something like:

class Fleet
{
    private Vehicle[] _vehicles;

    // returns the vehicles of the specified subclass
    public ???? Get(????)
    {
        return ????
    }
}

Fleet fleet = new Fleet("fleet.def");

Trains[] trains = fleet.Get(Trains);   // looks clean but isn't possible
Plains[] plains = fleet.Get<Plains>(); // looks okay but don't know
                                       //   how to implement

(I'm using arrays, but really any collection type that can be iterated is fine.)

Now, as you can see, I have absolutely no idea how to implement this. I'm looking for an elegant solution for the Get method, efficiency is not really an issue. Please also name the key techniques involved in the solution, so I can look them up in my C# books...

Thanks!

dh. · Accepted Answer · 2010-02-09 09:16:10Z

12

Your Fleet.Get() will look like

public IEnumerable<T> Get<T>()
{
  return _vehicles.OfType<T>();
}

answered Feb 9, 2010 at 9:16

dh.

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3 Comments

Fred K Over a year ago

Thanks a lot dh! Looks very clean. Now I can use "foreach (Plain plain in fleet.Get<Plain>()) { }. I guess that I can also use .ToList() and .ToArray() to store the result in a variable? What is this technique with the angle brackets called (yes, I am a n00b and not ashamed of it)?

dh. Over a year ago

That's called generics. The idea is to substitute a concrete type for reusability (for example when you have similar operations over different types). You can find out more in Introduction to Generics at msdn.microsoft.com/en-us/library/0x6a29h6.aspx

Fred K Over a year ago

Hmm, that's quite a generic name for such a specific thing :-) Thanks again, I have some reading to do...

Gerrie Schenck · Accepted Answer · 2010-02-09 09:14:39Z

1

Make it a List<> and use FindAll(x => x.GetType() == typeof(Train)) to get all Train objects from the list.

edited Feb 9, 2010 at 9:14

Gerrie Schenck

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answered Feb 9, 2010 at 9:10

Bolek Tekielski

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Comments

Naeem Sarfraz · Accepted Answer · 2010-02-09 09:17:42Z

0

 public T[] Get<T>() where T : Vehicle
 {
     List<Vehicle> lstVehicles = new List<Vehicle>(_vehicles);
     return lstVehicles.FindAll(delegate(Vehicle vehicle){
         return vehicle.GetType() == typeof(T);
     }).ToArray();
 }

answered Feb 9, 2010 at 9:17

Naeem Sarfraz

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