C# 实现自定义类型的A[key]取值

c#中怎么实现像Dictionary一样通过D[key]取值呢

public class Configuration<TKey,TValue>
    {
        private Dictionary<TKey, TValue> _dic = new Dictionary<TKey, TValue>();

        public TValue this[TKey key]
        {
            get
            {
                return _dic[key];
            }
            set
            {
                _dic[key] = value;
            }
        }

        public Configuration()
        {
            
        }

    }