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POIs it possible to create a truely weak-keyed dictionary in C#?
 

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    <p>I'm trying to nut out the details for a true <code>WeakKeyedDictionary&lt;,&gt;</code> for C#... but I'm running into difficulties.</p> <p>I realise this is a non-trivial task, but the seeming inability to declare a <code>WeakKeyedKeyValuePair&lt;,&gt;</code> (where the GC only follows the value reference if the key is reachable) makes it seemingly impossible.</p> <p>There are two main problems I see:</p> <ol> <li><p>Every implementation I've so far seen does not trim values after keys have been collected. Think about that - one of the main reasons for using such a Dictionary is to prevent those values being kept around (not just the keys!) as they're unreachable, but here they are left pointed to by strong references.</p> <p>Yes, add/remove from the Dictionary enough and they'll eventually be replaced, but what if you don't?</p></li> <li><p>Without a hypothetical <code>WeakKeyedKeyValuePair&lt;,&gt;</code> (or another means of telling the GC to only mark the value if the key is reachable) any value that refers to it's key would never be collected. This is a problem when storing arbitrary values.</p></li> </ol> <p>Problem 1 could be tackled in a fairly non-ideal/hackish way : use GC Notifications to wait for a full GC to complete, and then go along and prune the dictionary in another thread. This one I'm semi-ok with.</p> <p>But problem 2 has me stumped. I realise this is easily countered by a "so don't do that", but it has me wondering - is this problem even possible to solve?</p>
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