5

Extension methods with . operator always called, even if object is null without throwing NullReferenceException. By using operator ?. it will never called. For example: 

using System;

public class Program
{
    public static void Main()
    {
        A a = null;
        a.b(); // works
        a?.b(); // doesn't work
    }
}

public class A { }

public static class ext
{
    public static void b(this A a)
    {
        Console.WriteLine("I'm called");
    }
}

Why extension method isn't called in this case? Is this an ambiguos feature?

Konstantin Zadiran
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    You can see the compiled>decompiled code at [Try Roslyn](http://tryroslyn.azurewebsites.net/#f:r/K4Zwlgdg5gBAygTxAFwKYFsDcAobAHYAIwBswBjGM4gQxBBgAUAnAeyievWwG9sZ+YBEuRgpqyEQDcWYACYwAstUgAKAJR8BvATpgBBGNRgBeGBGDFiOXQOoA6QuswwA9C5gB3FkwDWITTbUAPwOTq7usiyoIBAA5Mie3j4BMAC+2On4RKQUVLT0BtxpuEI5osjiInl0MKgAHsg8KaUiYhIU0nIwjsgAFmAFhho62jYwAMIsECAsxKh2AOpMYGgAMpCoKgBEAJKx6JTUlqiyW2rWAumpQAAA) – Kobi Dec 30 '15 at 10:20
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    Well `?.` operator checks if value is `null` *before* doing anything, so why it should work ? Something to read : http://stackoverflow.com/questions/847209/in-c-what-happens-when-you-call-an-extension-method-on-a-null-object and https://msdn.microsoft.com/en-us/library/dn986595.aspx – Fabjan Dec 30 '15 at 10:23
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    What is the practical usage of having extension method which doesn't use this object at all. – Yeldar Kurmangaliyev Dec 30 '15 at 10:23
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    I don't understand why there is not `NullReferenceException` at `a.b();`? – Shaharyar Dec 30 '15 at 10:32
  • @Shaharyar, because nothing is being invoked on `a`. – Paulo Morgado Dec 30 '15 at 17:47

1 Answers1

16

Your expression a?.b() which uses ?. operator translates to equivalent:

if(a != null)
{
  a.b();
}

so this is why your method does not get called.

Marcin Zablocki
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