Non-repetitive way of saying: access this object's member unless the object is null

Question

Let's say I have a set of cars, where each car has a steering wheel. I'd like to write a line of code that looks for a car in the set and returns its steering wheel, or returns null if the car isn't in the set. Something like this:

Car found = // either a Car or null
SteeringWheel wheel = (found == null ? null : found.steeringwheel);

Is there a way to do this without using found and null twice in the expression? I don't like the smell of the repetition here.

score 7 · Answer 1 · answered May 01 '15 at 22:48

7

You could wait a bit for C# 6.0, and then use null-conditional (a.k.a. safe navigation) operator, ?.:

SteeringWheel wheel = FindCar()?.steeringwheel;

answered May 01 '15 at 22:48

AlexD

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score 3 · Accepted Answer · answered May 01 '15 at 22:58

3

There's not an obvious improvement until c# 6 arrives, but you could hide the unpleasantness in an extension method until then.

void Main() {
    Car found = null;// either a Car or null
    SteeringWheel wheel = found.MaybeGetWheel();
}

public static class CarExtensions {
    internal static SteeringWheel MaybeGetWheel(this Car @this) {
        return @this != null ? @this.steeringwheel : null;
    }
}

Some people say that you shouldn't allow extension methods to be called on null, but it does work. That's a style preference, not a technical limitation.

answered May 01 '15 at 22:58

recursive

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What's with the `@this` syntax? I've never seen that before. – Joe May 01 '15 at 23:01
I frequently do this with `ToString()`: `ToStringSafe()`. – dbc May 01 '15 at 23:02
`@this` just allows you to use "this" as an identifier instead of a keyword. – recursive May 01 '15 at 23:03
@dbc: Sometimes i use `string.Format("{0}", whatever)` to do that, as it tolerates nulls. – recursive May 02 '15 at 01:36

score 0 · Answer 3 · answered May 01 '15 at 23:15

0

Using linq you could do

var steeringwheel = cars.Where(c => c.name = "foo")
                        .Select(c => c.steeringwheel)
                        .SingleOrDefault();

answered May 01 '15 at 23:15

T I

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`.Where` only works on `IEnumerable`. – recursive May 01 '15 at 23:18
True, but this "looks for a car in a set and returns either a steering wheel or null if the car isn't in the set"? – T I May 01 '15 at 23:24

Non-repetitive way of saying: access this object's member unless the object is null

3 Answers3