CODEWITHSUNDEEP
c#operatorsnullable
Pal
Pal

Reputation: 776

Why nullable int (int?) doesn't increase the value via "+=" if the value is NULL?

I have a page counter type of int?:

spot.ViewCount += 1;

It works ONLY if the value of ViewCount property is NOT NULL (any int).

Why the compiler do so?

I would be grateful for any solutions.

Upvotes: 16

Views: 13931

Answers (4)

Jacob
Jacob

Reputation: 3698

You can use this extension method:

public static int? Add(this int? num1, int? num2)
{
    return num1.GetValueOrDefault() + num2.GetValueOrDefault();
}

Usage:

spot.ViewCount = spot.ViewCount.Add(1);

Or even:

int? num2 = 2; // or null
spot.ViewCount = spot.ViewCount.Add(num2);

Upvotes: 2

Patryk Ćwiek
Patryk Ćwiek

Reputation: 14318

Because nullable types have lifted operators. Generally, it's a specific case of function lifting in C# (or at least it looks like it is, correct me if I'm wrong).

Which means that any operation with null will have a null result (e.g 1 + null, null * null etc)

Upvotes: 4

keyboardP
keyboardP

Reputation: 69372

Null is not the same as 0. Therefore, there's no logical operation that will increase null to an int value (or any other value type). If you want to increase the value of a nullable int from null to 1, for example, you could do this.

int? myInt = null;
myInt = myInt.HasValue ? myInt += 1 : myInt = 1;

//above can be shortened to the below which uses the null coalescing operator ??
//myInt = ++myInt ?? 1

(although remember that this isn't increasing null, it's just achieving the effect of assigning an integer to a nullable int value when it's set as null).

Upvotes: 13

Denys Denysenko
Denys Denysenko

Reputation: 7894

If you'll look into what compiler has produced for you then you'll see the internal logic behind.

The code:

int? i = null;
i += 1;

Is actually threated like:

int? nullable;
int? i = null;
int? nullable1 = i;
if (nullable1.HasValue)
{
    nullable = new int?(nullable1.GetValueOrDefault() + 1);
}
else
{
    int? nullable2 = null;
    nullable = nullable2;
}
i = nullable;

I used JustDecompile to get this code

Upvotes: 7

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