Useful Things to Know, #425
You can call an extension method on a null class instance.
For example, if you have an extension method IsEmptyOrWhitespace on the class System.String, the following code will work:
string s = null;
Debug.Writeline(s.IsEmptyOrWhitespace());
It makes sense because the string s is actually passed as a parameter to the method IsEmptyOrWhitespace. Therefore, if you code the method correctly, it'll accommodate a null value and respond in whatever way makes sense.
It's interesting because it's a place where the facade of the extension method actually being an instance method of the class breaks down. (But I wouldn't code on the assumption that this will always be true!)
For example, if you have an extension method IsEmptyOrWhitespace on the class System.String, the following code will work:
string s = null;
Debug.Writeline(s.IsEmptyOrWhitespace());
It makes sense because the string s is actually passed as a parameter to the method IsEmptyOrWhitespace. Therefore, if you code the method correctly, it'll accommodate a null value and respond in whatever way makes sense.
It's interesting because it's a place where the facade of the extension method actually being an instance method of the class breaks down. (But I wouldn't code on the assumption that this will always be true!)
posted by Ann at 1:59 PM
3 Comments:
From what I have seen, 'most' (used loosely) people I have talked to say that passing null into an extension method should always throw a NullRef... but for String functions... it really helps a lot. +1 to you Ann!
Oh, I would agree: in the majority of cases, throwing an exception when a null object is passed to an extension method makes sense. But it's interesting and worth knowing that the runtime itself doesn't automatically throw one.
True that... I actually avoided that call... 'null'.ExtensionMethod for a while because of my NPE exception fear.
In reality, it's another one of the syntactic sugar calls that C# has and Java needs, along with 'var' ='''(
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