how to convert ConcurrentDictionary to Dictionary at runtime?

Question

I know how to convert a ConcurrentDictionary to a Dictionary.

And I know that I can use reflection to determine if an object contains a ConcurrentDictionary.

But after I determined that an object does have a ConcurrentDictionary via reflection, how do I convert it to a Dictionary at runtime? Or can I do it at all? It's going to change the definition of the class, right?

Edit: I should have made it more clear. I'll show an example:

    [Serializable]
    [DataContract]
    public class CacheItem
    {
        [DataMember]
        private ConcurrentDictionary<string, CacheItemEntity> _cacheItemDictionary = new ConcurrentDictionary<string, CacheItemEntity>();

        ......
    }

When I serialize an instance of this class, AVRO can't serialize the ConcurrentDictionary. So I wondered if I can convert the ConcurrentDictionary to a normal Dictionary at runtime. And this certainly changes the definition of the class. I'm just wondering if it can be done this way.

@jdphenix, to be able to serialize objects that contain ConcurrentDictionary via microsoft AVRO library. — Allen Zhang, Apr 29 '15 at 05:26
`var newDictionary = yourConcurrentDictionary.ToDictionary(kvp =>vp.Key, kvp => kvp.Value);` — Damith, Apr 29 '15 at 05:26
You can use `ToDictionary()` or the appropriate constructor of `Dictionary` as mentioned in comments. It's not really "converting" it though, but creating a new collection from a copy. If that's a good solution for you — jdphenix, Apr 29 '15 at 05:29
@Damith: perhaps you should cast yourConcurrentDictionary to ConcurrentDictionary first, since its type is known only at runtime. — Victor Mukherjee, Apr 29 '15 at 05:32
Your question is confusing, because you've said you know how to do A, and you know how to do B, but you want to know how to do B then A. Is the problem *actually* that you don't know the type arguments at compile-time, due to using reflection? What do you mean by "change the definition of the class" - are you trying to change the type of the field itself? It would really help if you could make this a lot clearer... — Jon Skeet, Apr 29 '15 at 05:36
DataContractSerializer (used by AVRO I believe) can serialize ConcurrentDictionary AFAIK. Why do you need to change it to Dictionary? — danish, Apr 29 '15 at 07:51
@JonSkeet, I edited my question. Hopefully it cleared things up a little. — Allen Zhang, Apr 29 '15 at 20:49
This sounds like it's quite an Avro-specific question - so that should be in your tags... my guess is that you should be implementing some specific serialization code. — Jon Skeet, Apr 29 '15 at 20:51
@JonSkeet, the motivation is AVRO. But I wonder if doing such thing is possible or not. — Allen Zhang, Apr 29 '15 at 20:59
Changing the type of a field (not just the value, but the actual *type* of a field)? Nope, basically not. Not unless you want to unload the appdomain, fiddle with the IL and reload it... — Jon Skeet, Apr 29 '15 at 21:00
[This question](http://stackoverflow.com/questions/18955441/how-to-serialize-deserialize-immutable-list-type-in-c-sharp)'s answers may have some useful advice in them. [This answer](http://stackoverflow.com/a/18957739/15880) in particular. — Powerlord, Apr 29 '15 at 21:00

score 3 · Answer 1 · edited Apr 29 '15 at 21:01

ConcurrentDictionary<TKey, TValue> implements IDictionary<TKey, TValue> so anyplace you are trying to use a "dictionary" you can use the interface instead. For example:

void ConsumeIDictionary(IDictionary dic)
{
   //perform work on a dictionary, regardless of the concrete type
}

You could call the method like this and it would be fine:

ConsumeIDictionary(new ConcurrentDictionary<int,int>());

Alternatively if you have a method that you want to use that requires the concrete Dictionary<TKey,TValue> type, then you can use the Dictionary constructor that takes an existing IDictionary:

void ConsumeDictionary<K,V>(Dictionary<K,V> dic)
{
   //perform work on a concrete Dictionary
}

Then call it like this:

ConsumeDictionary(
   new Dictionary(
       new ConcurrentDictionary<int,int>()));

Just be aware that calling this constructor is an O(n) operation.

If you are trying to using reflection, you can determine that an object is a ConcurrentDictionary by examining the object's type at runtime via GetType():

bool IsConcurrentDictionary<k, v>(obj o)
{
    return o.GetType() == typeof(ConcurrentDictionary<k,v>);
}

But in this case you may want to forget about the generic type parameters and just check for the IDictionary interface:

bool IsDictionary(obj o)
{
    return o is IDictionary;
}

how to convert ConcurrentDictionary to Dictionary at runtime?

1 Answers1