How I can understand when FirstOrDefault found nothing in sorted list?

Question

I have SortedList<DateTime, object>. Each times in it is a KeyValuePair<> which is a struct. So, how can I understand when method FirstOrDefault found nothing in this list ?(for classes it returns null but for a struct?)

Why I just cant compare default(KeyValuePair<Key, Value>) and result of FirstOrDefault?

private SortedList<DateTime, GatewayPassage> gwPassages = 
    new SortedList<DateTime, GatewayPassage>(new DescDateTimeComparer());

var lastGwPassages = gwPassages.FirstOrDefault(x => x.Value.Tag == tag &&
                                                    x.Value.Gateway == gateway);

I want condition like "if found nothing"

if(lastGwPassages == %some kind of default value%)

Why do you want to use FirstOfDefault if you want to control finding result? — ams4fy, Aug 03 '16 at 12:42
I think you should compare with `default(KeyValuePair)` instead — BytesOfMetal, Aug 03 '16 at 12:43
Can you provide some code to make sure we're understanding your question correctly? — sstan, Aug 03 '16 at 12:44
Please provide more actual code. Is the `default` value a value that can occur in the actual data? — Codor, Aug 03 '16 at 12:54

score 2 · Accepted Answer · answered Aug 03 '16 at 12:56

Cast the items into a KeyValuePair<DateTime,object>? and then you will be able to check if it is equals to null.

SortedList<DateTime, object> collection = new SortedList<DateTime, object>()
{
    {  new DateTime(2016,1,2), new object() },
    {  new DateTime(2016,1,1), new object() },
    {  new DateTime(2016,1,3), new object() },
};

var firstOrDefault = collection.Cast<KeyValuePair<DateTime,object>?>().FirstOrDefault(); // date of 1/1/2016
var checkIfDefault = firstOrDefault == null; // false

collection.Clear();

firstOrDefault = collection.Cast<KeyValuePair<DateTime, object>?>().FirstOrDefault(); // null
checkIfDefault = firstOrDefault == null; // true

In your example code:

var lastGwPassages = gwPassages.Cast<KeyValuePair<DateTime,GatewayPassage>?>()
                               .FirstOrDefault(x => x.Value.Tag == tag &&
                                                    x.Value.Gateway == gateway);

Now you can do lastGwPassages == null

How I can understand when FirstOrDefault found nothing in sorted list?

1 Answers1