Is there a C# class that provides map with weak keys or/and weak values? Or at least WeakHashMap like functionality.
+6
A:
The closest platform equivalent is probably a Dictionary<K, WeakReference<V>>. That is, it's just a regular dictionary, but with the values being weak references.
John Feminella
2010-01-17 16:01:58
You mixed something up, the keys have to be weak not the values, sorry just reread the question.
josefx
2010-01-17 16:10:46
It says "weak keys or/and weak values". Weak values are probably preferable to weak keys -- you don't want a weak key and a strong value, because then you don't have a way to get your value back if your key expires!
John Feminella
2010-01-17 16:13:24
Actually, weak keys are also very useful. For instance in caches.But they are harder to implement with just WeakReferences and Dictionary.
Daniel Sperry
2010-01-18 17:40:37
That's very true. If this was a cache, though, I don't think a WeakHashMap is necessarily what you want -- there are some better alternatives.
John Feminella
2010-01-18 17:57:51
For my current problem your solution is fine. I made a Dictionary<int, WeakReference>, and I might iterate over the key pairs from time to time to prune the collected values. However if I were more concerned with performance or concurrency this pruning would not be a such a good idea. WeakHashMap like (weak keys) also would not work. I asked the question trying to find the gold mine: some .net namespace with all nice gc aware collections and classes that I might need.In my previous project we built a STM system in java, there almost every possible combination of references were necessary.
Daniel Sperry
2010-01-19 11:33:31
+2
A:
In .Net 3.5 and below, there is no such structure available. However I wrote up one for a side project and posted the code at the following location
Starting in .Net 4.0, there is a structure available called ConditionalWeakHashTable in the Runtime.CompilerServices namespace that also does the trick.
JaredPar
2010-01-17 16:27:52
I recently came across this blog post It states "I'll save [compaction] for next time". I'm interested how compaction would be done, but I could not find "next time" :-( is it available anywhere? Here is what I came up with on my own: http://stackoverflow.com/questions/2047591
dtb
2010-01-17 16:39:36