FirstOrDefault() result of a struct collection?

Question

So I've got a collection of structs (it's actually a WCF datacontract but I'm presuming this has no bearing here).

List<OptionalExtra> OptionalExtras;

OptionalExtra is a struct.

public partial struct OptionalExtra

Now I'm running the below statement:

OptionalExtra multiOptExtra = OptionalExtras.Where(w => w.Code == optExtra.Code).FirstOrDefault();
if (multiOptExtra != null)
{

}

Now this won't compile:

the operator != cannot be applied to opperands of type OptionalExtra and '<null>'

After a little googling I realised it's because OptionalExtra is a struct. Which I believe is not nullable unless defined as a nullable type?

So my question is, if my where statement returns no results what will be the outcome of the FirstOrDefault call? Will it thrown an exception?

Incidently this should never happen but better safe than sorry.

Answer 1

If default(OptionExtra) is still a valid value, it's better to change your code to this

var results = OptionalExtras.Where(w => w.Code == optExtra.Code).Take(1).ToList();
if (results.Any()) {
   multiOptExtra = results[0]
}

Answer 2

Assuming Code is a string for the purposes of my answer, you should be able just to test that value for its default.

OptionalExtra multiOptExtra = OptionalExtras.Where(w => w.Code == optExtra.Code).FirstOrDefault();
if (multiOptExtra.Code != null)
{

}

Answer 3

its provide you defualt value for your structure like as below

int[] numbers = { };
int first = numbers.FirstOrDefault();
Console.WriteLine(first);//this print 0 as output 

other option to handle is make use of default value like as below

List<int> months = new List<int> { };
// Setting the default value to 1 by using DefaultIfEmpty() in the query. 
int firstMonth2 = months.DefaultIfEmpty(1).First();
Console.WriteLine("The value of the firstMonth2 variable is {0}", firstMonth2);

Answer 4

As others have said, the result of your code when no elements match will be:

default( OptionalExtra )

If you want a null returned, you can cast your list to OptionalExtra?

OptionalExtra? multiOptExtra = OptionalExtras.Cast<OptionalExtra?>().Where( ...

You can then test for null

Answer 5

If you want to check for null, use System.Nullable collection:

var OptionalExtras = new List<OptionalExtra?>();
/* Add some values */
var extras = OptionalExtras.FirstOrDefault(oe => oe.Value.Code == "code");
if (extras != null)
{
    Console.WriteLine(extras.Value.Code);
}

Note that you have to use Value to access the element.

Answer 6

The result will be the default value of your struct, e.g. default(OptionalExtras).

Whereas for a reference type the default value is null.