Good implementation of weak dictionary in .Net

Question

Where can I find good implementation of IDictionary which uses weak references inside?

Dictionary should be holding only weak references to values and eventually clean up itself of dead references.

Or should I just write it myself?

Answer 1

ConditionalWeakTable Class uses weak keys and automatically removes the key/value entry as soon as no other references to a key exist outside the table.

Answer 2

You'll need to write it yourself. It should be relatively straight forward, implementing the IDictionary<T,T> interface and then storing the actual values as WeakReferences<T>. You can then check the values on add/select using TryGetTarget to see if they're still alive.

public class WeakDictionary <TKey,TValue> : IDictionary<TKey,TValue>     where TValue : class {     private readonly Dictionary<TKey,WeakReference<TValue>> innerDictionary = new Dictionary<TKey,WeakReference<TValue>>();               public TValue Index[ TKey key ]     {         get         {             // Use .TryGetTarget instead of .IsAlive and .Target             if (this.innerDictionary.TryGetValue(key, out WeakReference<TValue> wf) && wf.TryGetTarget(out TValue value))             {                 return value;             }              return null;         }              }          private void Cull()     {         var deadKeys = this.innerDictionary.Where(kvp => kvp.Value.IsAlive).Select(kvp => kvp.Key).ToList();          foreach (var key in deadKeys)         {             _ = this.innerDictionary.TryRemove(key);         }     } }