Is it possible to assign a value to a nullable using the conditional operator?

Question

I know I can do this:

Int32 tempInt;
Int32? exitNum;

if (Int32.TryParse(fields[13], out tempInt))
    exitNum = tempInt;
else
    exitNum = null;

But why can't I do this?

Int32 tempInt;
Int32? exitNum = Int32.TryParse(fields[13], out tempInt) ? tempInt : null;

Is there a way to assign a value to a nullable using the conditional operator?

What does the coalescing operator have to do with your question? The question appears to be about the conditional operator, not the coalescing operator. — Eric Lippert, Jul 14 '11 at 15:13
possible duplicate of [c# why cant a nullable int be assigned null as a value](http://stackoverflow.com/questions/330471/c-why-cant-a-nullable-int-be-assigned-null-as-a-value) — Eric Lippert, Jul 14 '11 at 18:32

score 11 · Accepted Answer · answered Jul 14 '11 at 14:31

11

One side of the conditional operator must be convertible to the type of the other side.
In your case, you have an int on one side, and null (a type-less expression) on the other side. Since neither side is directly compatible with the other side, it doesn't work.

You need to make sure that at least one side is an int?, either by casting, or by writing new int?().

Write Int32.TryParse(fields[13], out tempInt) ? tempInt : new int?()

answered Jul 14 '11 at 14:31

SLaks

868,454
176
1,908
1,964

2

Another option is to use `default(int?)` instead of `new int?()`. – svick Jul 14 '11 at 17:34
1

`new int?()` just seems wrong; it's a matter of style, but I'd much prefer `default(int?)` or `(int?)null`. – configurator Jul 14 '11 at 23:21

score 6 · Answer 2 · answered Jul 14 '11 at 15:11

As others have noted, you have to insure that there is a consistent return type present in the conditional operator. (A subtle feature of C# is that when we must produce a type for an expression amongst several alternatives, the chosen alternative is always somewhere in the expression; we never "magic up" a type that didn't appear.)

If unusual facts about the conditional operator interest you, I recommend my articles on the subject:

http://blogs.msdn.com/b/ericlippert/archive/tags/conditional+operator/

I would add that this is a great opportunity to write an extension method:

static class MyExtensions
{
    public static int? ParseInt(this string s)
    {
        int value;
        return Int32.TryParse(s, out value) ? value : (int?)null;
    }
}

And now you can just say

int? exitNum = fields[13].ParseInt();

which is much more pleasant to read.

score 1 · Answer 3 · answered Jul 14 '11 at 14:38

1

You just need to do a cast to Int32? on tempInt

Int32? exitNum = Int32.TryParse(fields[13], out tempInt) ? (int?)tempInt : null;

answered Jul 14 '11 at 14:38

Jeff LaFay

12,882
13
71
101

score 0 · Answer 4 · answered Jul 14 '11 at 14:48

0

You can cast null to int? so that both sides have same type:

Int32 tempInt;
Int32? exitNum = Int32.TryParse(fields[13], out tempInt) ? tempInt : (int?)null;

answered Jul 14 '11 at 14:48

Răzvan Flavius Panda

21,730
17
111
169

Is it possible to assign a value to a nullable using the conditional operator?

4 Answers4