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POReturning null from C# generic regardless of supplied type
 

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  1. POReturning null from C# generic regardless of supplied type
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    <p>I'm writing an in-memory cache of settings for our webservices. This is so that we do not have to hit the database every time we need a setting. We have a mechanism to invalidate the cache when the database is updated.</p> <p>The cache is a bunch of dictionaries that contain different types, here's two of those dictionaries:</p> <pre><code>static readonly object StringValueCacheMutex = new object(); static readonly Dictionary&lt;string, Dictionary&lt;string, string&gt;&gt; StringValueCache = new Dictionary&lt;string, Dictionary&lt;string, string&gt;&gt;(); static readonly object IntegerValueCacheMutex = new object(); static readonly Dictionary&lt;string, Dictionary&lt;string, Int64&gt;&gt; IntegerValueCache = new Dictionary&lt;string, Dictionary&lt;string, Int64&gt;&gt;(); </code></pre> <p>I would like to write a generic function that gets a value from these dictionaries, if the category/setting was not found in the dictionary it should return null to signify it was not found. </p> <p>The problem is that these dictionaries contain both nullable and non-nullable types.</p> <p>Here's the generic I want to have:</p> <pre><code>public static TValue GetValueOrNull&lt;TValue&gt;( IDictionary&lt;string, Dictionary&lt;string, TValue&gt;&gt; cacheDictionary, object cacheMutex, string categoryName, string settingName) { TValue value = null; lock (cacheMutex) { if (cacheDictionary.ContainsKey(categoryName)) { if (cacheDictionary[categoryName].ContainsKey(settingName)) { value = cacheDictionary[categoryName][settingName]; } } } return value; } </code></pre> <p>This will not compile due to : "Cannot convert null to type parameter 'TValue' because it could be a non-nullable value type. Consider using 'default(TValue)' instead."</p> <p>The reason I want to return null and not default(TValue) is that in the case of an integer, the caller has no way of knowing if the setting value was actually 0 or of it was not found in the cache.</p> <p>So my question is, is there constraints I can put on a generic that will allow me to return null regardless of the supplied type? (I'm assuming I need to use Nullable but not sure how.</p>
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    1. CONot related to your particular question, but you might consider a `ReadWriterLock` (or better a `ReaderWriterLockSlim`,) since there's probably not a good reason for multiple readers to block one another.
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