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Asked: 2026-05-11T03:47:08+00:00

I really hate sometimes how IDictionary<TKey, TValue> [key] will throw an exception if the

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I really hate sometimes how IDictionary<TKey, TValue> [key] will throw an exception if the key doesn’t exist in the dictionary.

Of course there is TryGetValue(), but that seems to have been optimized for performance and not usability.

So I thought, oh I’ll just make an extension method for it – which I did :

public static class CollectionExtensions {     public static TType GetValueOrDefault<TKeyType, TValue, TType>(this IDictionary<TKeyType, TType> dictionary, TKeyType key)     {         TType value = default(TType);          // attempt to get the value of the key from the dictionary         // if the key doesn't exist just return null         if (dictionary.TryGetValue(key, out value))         {             return value;         }         else         {             return default(TType);         }     }     }

This works fine EXCEPT I cannot seem to get type inference working.

Obviously I want to be able to do the following :

var extraDataLookup = new Dictionary<string, string>(); extraDataLookup['zipcode'] = model.Zipcode;

and then be able to access the value :

var zipcode = extraDataLookup.GetValueOrDefault('zipcode'); var foo = extraDataLookup.GetValueOrDefault('foo'); // should be null

I’ve looked at a few things about type inference, inlucing Jon Skeet’s article and even sourcecode to System.Linq.Enumerable in reflector but seem to be missing something.

This works :

extraDataLookup.GetValueOrDefault<string, string,string> ('foo')

but this doesn’t

extraDataLookup.GetValueOrDefault ('foo')

What should I be doing.

PS. I’m only looking for solutions to the generic type inference problem, not any other suggestions. Thanks.

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1 Answer

  1. You seem to be defining your extension method with three generic types when you only need two. ‘TValue’ and ‘TType’ mean the same thing, don’t they? Try this:

    public static TValue GetValueOrDefault<TKey, TValue>(     this IDictionary<TKey, TValue> dictionary, TKey key) {     TValue value;     // attempt to get the value of the key from the dictionary     dictionary.TryGetValue(key, out value);     return value; }
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