IsNullOrWhiteSpace() was added in dot net 4: http://msdn.microsoft.com/en-us/library/system.string.isnull...

I agree that Truncate would be a nice one to include in the core.

> IsNullOrWhiteSpace() was added in dot net 4:

Look at what the helper actually does. I already addressed this in my comment.

     string hello = magic();    
     if(hello.IsNullOrWhiteSpace()) 
     { ... }

Is significantly more intuitive than:

     string hello = magic(); 
     if(string.IsNullOrWhiteSpace(hello))
     { ... }

Plus it is consistent with things like Contains("XYZ") (e.g. hello.Contains("something")).

Truncate is useful just because Substring() throws a bunch of dumb exceptions. It is mostly a workaround for Substring's poor design.

That defeats half the purpose though, because if the string is null, you won't be able to call the method without throwing an exception. Or is that not the case for extension methods?

Extension methods are rewritten by the compiler to a normal static method call with the subject as their first argument (that's how they're defined, anyway). And since you can legitimately pass null to those methods there will be no NRE by default.

Calling IsNullOrWhiteSpace on an instance looks even more counter-intuitive to me, though – it wouldn't work on null if it were a real instance method.

It is consistent with how other .Net libraries work (particularly the string ones). It also works fine on null as long as the type of null is string.

It works because it's an extension method, but aren't extension methods supposed to make things nice and consistent by making it look as if you're calling an instance method?

Since this would be completely broken if it were an instance method, the reader might be surprised at first until they realize it's an extension method. So all I'm saying is that it's no less "counter-intuitive" than the normal string.IsNullOrWhiteSpace.

Indeed, the fact that extension methods happen to work with `this == null` is more of a bonus feature than something that should be deliberately used.