Is there a shorthand for addition assignment operator for nullables that sets the value if null?

Question

I am using nullable doubles to store the sum of some values pulled from various sources. The sum could be any real value or null if no elements are present.

Currently, I use a null check and either assign or increment:

double? sum = null;
...    
if(sum == null)
    sum = someTempValue;
else
    sum += someTempValue;

I know c# has several shorthand null checks for method calls and the such. My question is if there is a shorthand notation to the addition assignment operator += when using nullables that assigns the value if null or performs the operation if not null?

More info on the '?' operator: https://msdn.microsoft.com/en-gb/library/ty67wk28.aspx — sr28, May 18 '16 at 09:19
@Patrick Hofman Nothing is wrong with the if statement. I was just wondering if there was a shorthand for this. I find c# has a ton of short-handedness for nulls and was wondering if one existed for this. Plus this is for a data skimmer and even a few of these gets a little messy. — Lithium, May 18 '16 at 09:19
If you're sticking in loads of `if statements` everywhere then it sounds like you need to rethink you're design rather than worrying about shorthand null checks. — sr28, May 18 '16 at 09:23

score 3 · Accepted Answer · edited May 23 '17 at 10:28

3

You could put ternary operator:

double? sum = null;
sum = sum == null ? someTempValue : sum + someTempValue;

Or

sum = someTempValue + (sum == null ? 0 : sum);

Or

sum = someTempValue + (sum ?? 0);

Credit to: Dmitry Bychenko for the last option

edited May 23 '17 at 10:28

Community

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answered May 18 '16 at 09:15

Ian

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That is not a shorthand for the addition assignment operator as OP asked, but I guess that is the shortest code possible. – Patrick Hofman May 18 '16 at 09:17
Ah yes, it is fitter to say that this is shortest code possible rather than shorthand for the addition assignment – Ian May 18 '16 at 09:19
1

`sum = someTempValue + (sum ?? 0);` – Dmitry Bychenko May 18 '16 at 09:22
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@Ian: a typical use of *ternary operator* (when `if else` brings only *complexity*, but not *readability*). +1 – Dmitry Bychenko May 18 '16 at 09:32
ah yes, it is exactly as you said. :) – Ian May 18 '16 at 09:34

score 1 · Answer 2 · answered May 18 '16 at 09:23

1

Not a real shortcut, but quite compact:

sum = sum ?? 0 + someTempValue;

treat sum as 0 when sum == null. But, please, notice that ?? operator can be dangerous:

// parenthesis () are mandatory, otherwise you'll have a wrong formula
// (someTempValue + sum) ?? 0;
sum = someTempValue + (sum ?? 0);

answered May 18 '16 at 09:23

Dmitry Bychenko

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upvoted, as the last option of my answer is from your comment – Ian May 18 '16 at 09:28
@Ian: I've answered just to show up that `??` solution being a *compact* has a *flaw*: it's easy to get a wrong formula. – Dmitry Bychenko May 18 '16 at 09:30

score 0 · Answer 3 · answered May 19 '16 at 07:55

It's not quite clear from the post, but looks like the someTempValue is non nullable, otherwise the if logic will not work because + operator will destroy the previous sum if the someTempValue is null.

If that's true, then you can utilize the null-coalescing operator and the fact that null + value == null:

sum = (sum + someTempValue) ?? someTempValue;

If someTempValue is also nullable, then the correct logic would be:

sum = (sum + someTempValue) ?? someTempValue ?? sum;

IMO, with shorthand or not, it's better to put that logic in a method

public static class MathUtils
{
    public static double? Add(double? left, double? right)
    {
        // The avove shorthand
        return (left + right) ?? right ?? left;
        // or another one
        //return left == null ? right : right == null ? left : left + right;
    }
}

and use simple

sum = MathUtils.Add(sum, someTempValue);

or with C#6 using static feature, the even shorter

sum = Add(sum, someTempValue);

Is there a shorthand for addition assignment operator for nullables that sets the value if null?

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