Question

I have a class that contains something like this Dictionary<int, Queue<string>> dict and then I use TryGetValue:

Queue<string> value;
if (!dict.TryGetValue(3, out value))
    throw new MyException("...");

Is there an option not to explicitly define the value type, basically to avoid duplicity of typing it? In C++ STL containers, there is a value typedef value_type which can be used in such cases but I can’t seem to find similar feature in C#. Thanks.

Answer 1

If you define yourself a nice helper method, you can wrap up the type specification:

public static class Utility
{
    public static TValue GetValueOrDefault<TKey,TValue>(
        this Dictionary<TKey, TValue> dictionary, 
        TKey key, 
        TValue @default = default(TValue))
    {
        TValue value;
        return dictionary.TryGetValue(key, out value)
                   ? value
                   : @default;
    }
}

Notice here we still have to explicitly type the value that’s going to be populated by TryGetValue, BUT from your caller you can just say:

var value = dict.GetValueOrDefault(3);    // implicitly typed
if (value == null)
    throw new MyException("...");

Note that if null is a valid value in this context, you’ll need something else, but the same principle could be applied – use the fact that the compiler can infer types for generic methods to build a helper method to hide the explicit typing.