c# virtual dictionary?

Question

I have a class with a dictionary object. Any class that derives from that class, I want to override the dictionary with it's own implementation.

How can this be achieved as the virtual keyword is not valid here?

Thanks.

Answer 1

You can't have virtual fields, but you can have virtual properties.

Additionally, it would be a good idea to declare the property-type to be of the IDictionary<TKey, TValue> interface rather than the Dictionary<TKey, TValue> concrete- type, since this class is not designed for inheritance.

E.g:

private readonly Dictionary<string, int> _myDictionary 
                  = new Dictionary<string, int>();

protected virtual IDictionary<string, int> MyDictionary 
{
   get
   {
      return _myDictionary; 
   }
}

Subclasses will not see the field; only the property will be visible. They are free to override the property and provide their own implementation; for example by returning an instance of a custom-type that implements the interface.

Answer 2

Something like this should work:

public class Base
{
    private Dictionary<string, string> dictionary = new Dictionary<string, string>();

    public virtual IDictionary<string, string> DictInstance
    {
        get { return this.dictionary; }
    }
}

public class Derived : Base
{
    private MySpecialDictionary otherDictionary = new MySpecialDictionary();

    public override IDictionary<string, string> DictInstance
    {
        get { return this.otherDictionary; }
    }
}