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+---- Thread: [C#] [NotNull] attribute for parameters. (/showthread.php?tid=5318349)
[NotNull] attribute for parameters. - severos - Jun 26, 2016
I'm writing couple methods that take objects as parameters, currently I'm doing a manual if(obj==null) throw exception/return error. but I've noticed in some built in methods (Encoding.ASCII.GetBytes for example), the parameter have a [NotNull] attribute, any idea how I can get that into my code? tried applying the attribute but can't find it.
* - ubbelol - Jun 26, 2016
Not sure about that attribute, but you can do something similar with code contracts:
![[Image: f58329c9b4eebc2f03f1c2fad4d55f74.png]](https://i.gyazo.com/f58329c9b4eebc2f03f1c2fad4d55f74.png)
https://msdn.microsoft.com/en-us/library/dd264808(v=vs.110).aspx
* - severos - Jun 26, 2016
(Jun 26, 2016 06:37 AM)ubbelol Wrote: Not sure about that attribute, but you can do something similar with code contracts:
https://msdn.microsoft.com/en-us/library/dd264808(v=vs.110).aspx
A fast reading shows that it's what I want (validate argument isn't null), I'll be taking deeper look at it soon.
Thanks for the help :D
* - caesay - Jun 30, 2016
The attributes are merely hints to the caller that the method has a certain requirement (NotNull or CanBeNull). Presumably, these attributes assist Microsoft and the CLR team in enforcing code contracts and doing unit tests.
In C#6 and roslyn i believe these attributes are internal-only, so they've been deprecated.
Some extensions / libraries have their own NotNull attributes - such as Resharper. If you include the JetBrains.Annotations library, you get [notnull] and [canbenull] and many other attributes, and if the consumer of the library has Resharper installed, they will get visual cues if they try to pass in a potential null value as a [NotNull] method parameter.
In summary, these attributes are for code contracts, and are not an excuse to skip doing null checks in your methods.