Tuesday, May 02, 2006

(.NET 2.) Dictionary(Of Key, Value) performance trick

by FransBouma via Frans Bouma's blog on 5/2/2006 2:52:00 PM

(I used the VB.NET notation in the title so it won't nag about illegal characters like < and >)

In .NET 2.0 you'll have this new generic Hashtable variant called Dictionary<TKey, TValue>. It can be used as a Hashtable but now strongly typed and it doesn't use boxing anymore with value types. That's great and all, though there's one thing that's different from the hashtable: retrieving a value with a key that's not there. If the key value isn't present in the Dictionary, you'll get an exception when you do:

MyClass myValue = myDictionary[key];

What's often overlooked is a performance penalty with this pattern shift. Because of the exception, people will do something like this:

MyClass toReturn;
if(!_myDictionary.ContainsKey(key))
{
	toReturn = _myDictionary[key];
}
else
{
	toReturn = new MyClass();
}

MyClass toReturn = null;
if(!_myDictionary.TryGetValue(key, out toReturn))
{
	toReturn = new MyClass();
}

About the lack of blogging lately: I was very busy with finalizing the beta for LLBLGen Pro v2.0, which first beta was released 2 days ago. It's still pretty hectic, but I hope to have more time soon to blog more!