Nullable value types

Question

If a value type is declared nullable, how should I take precautions for this? I.e. if in the constructor I have:

public Point3 ( Point3 source )
{
    this.X = source.X;
    this.Y = source.Y;
    this.Z = source.Z;
}

would it fail, if source was null?

Answer 1

I don't see the possibility of Point3 being null if it's a value type. Don't you miss a question mark? And if you really mean Point3?, then you should access it like:

public Point3 ( Point3? source )
{
    this.X = source.Value.X;
    this.Y = source.Value.Y;
    this.Z = source.Value.Z;
}

and in this case, the Value property will throw an exception if it's null.

Answer 2

Yes, that would fail if source was null.

You'll have to decide what the correct behavior should be if source is null. You might just throw an exception.

public Point3 ( Point3? source )
{
    if (source == null) 
    {
        throw new ArgumentNullException("source");
    }

    this.X = source.Value.X;
    this.Y = source.Value.Y;
    this.Z = source.Value.Z;
}

Or, if you don't want to accept null values for source, just keep the method as you have it in your example. That method doesn't accept a Nullable<Point3>, so you don't have to worry about it being null in that case.

Answer 3

The caller of this method will not be able to pass in a nullable point, since the method takes a regular point, not a Nullable one. Therefore, you don't need to worry about Point being null in your constructor code.

Answer 4

If source was a Point3? it wouldn't be a Point3. So as far as I know, it would fail compile time. To send in a Point3? you would have to use .Value, which would throw an exception I believe if it was null.

Answer 5

    public Point3(Point3? source) { 
       this.X = source.GetValueOrDefault().X; 
        this.Y = source.GetValueOrDefault().Y;
        this.Z = source.GetValueOrDefault().Z; 
    }