C#

namespace TryWeakDictionary{
    public class WeakReference<T> : WeakReference {
        public WeakReference(T val)
	    : base(val, false) {
        }
    }

    public class WeakDictionary<TKey, TValue> : IDictionary<TKey,TValue> {
        private Dictionary<TKey, WeakReference<TValue>> weakDictionary = new 
                   Dictionary<TKey, WeakReference<TValue>>();
		
        public void Add(TKey key, TValue value) {
            WeakReference<TValue> weakRef = new WeakReference<TValue>(value);
	    this.weakDictionary.Add(key, weakRef);
        }

        public void Clear() {
            this.weakDictionary.Clear();
	}

        public bool ContainsKey(TKey key) {
	    return this.weakDictionary.ContainsKey(key);
        }

        public void Remove(TKey key) {
	    this.weakDictionary.Remove(key);
        }

        public bool TryGetValue(TKey key, out TValue value) {
	    WeakReference<TValue> weakReference;
	    if (this.weakDictionary.TryGetValue(key, out weakReference) &&  
                weakReference.IsAlive) {
		    value = (TValue)weakReference.Target;
		    return true;
	    } else {
		weakDictionary.Remove(key);
		value = default(TValue);
		return false;
	    }
        }
    }
}