C# Generic Identity Map -- Creating an Object Pool for Multiple Object Types

public bool RemoveItem<T>(Int32 pID)
{
Type myType = typeof(T);

if (!m_pool.ContainsKey(myType))
return false;

if (!m_pool[myType].ContainsKey(pID))
return false;

return m_pool[myType].Remove(pID);
}

If these two methods are the only way to add and remove items from the pool then we can be sure of the type of the object in the inner Dictionary<Int32, Object>. This allows us to have one identity map object for all our loaded objects. So we can have on method to retrieve any object in the pool:

public T GetItem<T>(Int32 pID)
{
// will throw KeyNotFoundException if either of the dictionaries
// does not hold the required key
return (T) m_pool[myType][pID];
}

The thing to be careful of is if you have a long inheritance chains in your object model, you could enter an object in the pool under many different "type" keys and not know how to retrieve the objects put into your dictionary. Being aware of this, you have to be sure to use consistent types with each method call.

Here is how we would use our aggregate pool:

class Program
{
public static ObjectPool pool = new ObjectPool();

static void Main(string[] args)
{
Animal dog = new Animal() { Name = "Fido", ID = 1 };
Vegetable carrot = new Vegetable { Color = "Orange", Identifier = 1, IsTasty = true };
Mineral carbon = new Mineral() { UniqueID = 2, IsPoisonousToAnimal = false };

pool.AddItem<Animal>(dog.ID, dog);
pool.AddItem<Vegetable>(carrot.Identifier, carrot);
pool.AddItem<Mineral>(carbon.UniqueID, carbon);

Console.WriteLine("Dog is in the pool -- this statement is " + pool.ContainsKey<Animal>(dog.ID));
Console.ReadLine();
}
}

Until next time,
Happy coding