Update dictionary value and get the previous one in C#

Question

I've came to C# world from Java background.

I need to update the value in a map/dictionary and get the previous value (or null if there were none). I would do the following in Java:

String oldValue = myMap.put(key, newValue);
someFunction(oldValue, newValue);

In C# I use Dictionary, but I've found no method to get the previous value on update. So far I need to perform 2 lookups to accomplish this, which I see not very optimal in terms of performance and lines of code

string oldValue = null;
myDictionary.TryGetValue(key, oldValue);
myDictionary[key] = newValue;
SomeFunction(oldValue, newValue);

Is there an easier way to update value and get the previous one?

Answer 1

public static class DictionaryExtensions
{
    public static TValue UpdateAndGet<TKey, TValue>(this Dictionary<TKey, TValue> dictionary, TKey key, TValue newVal)
    {
        TValue oldVal;
        dictionary.TryGetValue(key, out oldVal);
        dictionary[key] = newVal;

        return oldVal;
    }
}