Dictionary returning a default value if the key does not exist
c#, collections, dictionary
Solution
As per comments, in .Net Core 2+ / NetStandard 2.1+ / Net 5, MS added the extension method GetValueOrDefault()
`TryGetValue` will already assign the default value for the type to the dictionary, so you can just use:
dictionary.TryGetValue(key, out value);
and just ignore the return value. However, that really will just return `default(TValue)`, not some custom default value (nor, more usefully, the result of executing a delegate). There's nothing more powerful built into the framework. I would suggest two extension methods:
public static TValue GetValueOrDefault<TKey, TValue>(
this IDictionary<TKey, TValue> dictionary,
TKey key,
TValue defaultValue)
{
return dictionary.TryGetValue(key, out var value) ? value : defaultValue;
}
public static TValue GetValueOrDefault<TKey, TValue>(
this IDictionary<TKey, TValue> dictionary,
TKey key,
Func<TValue> defaultValueProvider)
{
return dictionary.TryGetValue(key, out var value) ? value : defaultValueProvider();
}
(You may want to put argument checking in, of course :)
Problem
I find myself using the current pattern quite often in my code nowadays ``` var dictionary = new Dictionary<type, IList<othertype>>(); // Add stuff to dictionary var somethingElse = dictionary.ContainsKey(key) ? dictionary[key] : new List<othertype>(); // Do work with the somethingelse variable ``` Or sometimes ``` var dictionary = new Dictionary<type, IList<othertype>>(); // Add stuff to dictionary IList<othertype> somethingElse; if(!dictionary.TryGetValue(key, out somethingElse) { somethingElse = new List<othertype>(); } ``` Both of these ways feel quite roundabout. What I really would like is something like ``` dictionary.GetValueOrDefault(key) ``` Now, I could write an extension method for the dictionary class that does this for me, but I figured that I might be missing something that already exists. SO, is there a way to do this in a way that is more "easy on the eyes" without writing an extension method to dictionary?