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Asked: 2026-05-10T20:55:52+00:00

Is there a simple attribute or data contract that I can assign to a

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Is there a simple attribute or data contract that I can assign to a function parameter that prevents null from being passed in C#/.NET? Ideally this would also check at compile time to make sure the literal null isn’t being used anywhere for it and at run-time throw ArgumentNullException.

Currently I write something like …

if (null == arg)   throw new ArgumentNullException('arg');

… for every argument that I expect to not be null.

On the same note, is there an opposite to Nullable<> whereby the following would fail:

NonNullable<string> s = null; // throw some kind of exception
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  1. There’s nothing available at compile-time, unfortunately.

    I have a bit of a hacky solution which I posted on my blog recently, which uses a new struct and conversions.

    In .NET 4.0 with the Code Contracts stuff, life will be a lot nicer. It would still be quite nice to have actual language syntax and support around non-nullability, but the code contracts will help a lot.

    I also have an extension method in MiscUtil called ThrowIfNull which makes it a bit simpler.

    One final point – any reason for using ‘if (null == arg)‘ instead of ‘if (arg == null)‘? I find the latter easier to read, and the problem the former solves in C doesn’t apply to C#.

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