This is a .NET 4 Dynamic Dictionary

DynamicDictionary.cs

public class DynamicDictionary : DynamicObject
{
  private Dictionary<string, object> _members = new Dictionary<string, object>();

  public bool IsEmpty()
  {
    if (_members.Keys.Count() > 0)
    {
      return false;
    }

    return true;
  }

  public override IEnumerable<string> GetDynamicMemberNames()
  {
    return _members.Keys;
  }

  public IEnumerable<string> GetDynamicMemberNames(string key)
  {
    if (_members.ContainsKey(key))
    {
      if (_members[key] is DynamicDictionary)
        return (_members[key] as DynamicDictionary)._members.Keys;
    }

    return null;
  }

  public Dictionary<string, object> GetDynamicDictionary()
  {
    return _members;
  }

  public Dictionary<string, object> GetDynamicDictionary(string key)
  {
    if (_members.ContainsKey(key))
    {
      if (_members[key] is DynamicDictionary)
        return (_members[key] as DynamicDictionary)._members;
    }

    return null;
  }

  public override bool TrySetMember(SetMemberBinder binder, object value)
  {
    if (!_members.ContainsKey(binder.Name))
    {
      _members.Add(binder.Name, value);
    }
    else
    {
      _members[binder.Name] = value;
    }

    return true;
  }

  public override bool TryGetMember(GetMemberBinder binder, out object result)
  {
    if (_members.ContainsKey(binder.Name))
    {
      result = _members[binder.Name];
    }
    else
    {
      result = _members[binder.Name] = new DynamicDictionary();
    }

    return true;
  }
}