要简化键为元组时对字典的C＃访问

Question

Is there a simpler way to check a dictionary where the key is a tuple and then assign the value you were just checking for to a variable? I've got the following code that works, but it seems tedious.

int hitCount = dict.ContainsKey(new Tuple<string, string>(tr, "H"))
   ? dict[new Tuple<string, string>(tr, "H")]
   : 0;

Answer 1

int hitCount;
var key = new Tuple<string, string>(tr, "H");
dict.TryGetValue(key, out hitCount);

Starting with C# 7:

var key = new Tuple<string, string>(tr, "H");
dict.TryGetValue(key, out int hitCount);

The difference is that the declaration of hitCount is moved to the place where it's used as an out parameter.

It's obviously not really necessary to define the key in a separate variable, but in these scenarios you're likely going to want to add the key if it doesn't exist.

Answer 2

Use Tuple.Create to let the compiler infer generic type parameters from the type of method arguments:

int hitCount;
if (!dict.TryGetValue(Tuple.Create(tr, "H"), out hitCount)) {
    hitCount = 0;
}

Note: Setting hitCount to zero is not necessary. This code illustrates how to deal with missing keys, in case you wish to use a different number as a default.

Answer 3

Use Dictionary<K,V>.TryGetValue :

int hitCount;
dict.TryGetValue(new Tuple<string, string>(tr, "H"), out hitCount);

If the value is not found, hitCount will be assigned to int 's default value, that is 0 .

Answer 4

In the off-chance this might help others, with C# 7.0 you can declare and even name the fields in your tuple, and easily retrieve those values for logging or other manipulation.

var tupleKey = (FirstParam: tr, SecondParam: "H");

if (dict.ContainsKey(tupleKey))
{
     _logger.Log($"Found key using {tupleKey.FirstParam} and {tupleKey.SecondParam}.");
     return dict[tupleKey];
}
return 0;

Or for quick recall:

dict.TryGetValue(tupleKey, out int hitCount);