C#: How to Implement and use a NotNull and CanBeNull attribute

Question

I want to let programmers and myself know that a method does not want null and if you do send null to it anyways, the result will not be pretty.

Answer 1

As pointed by Anton Gogolev, attributes can be created using PostSharp.(note that CodeContract is using static method calls inside body of method)

UPDATE Feb 2013: new 3.0 release of PostSharp (currently in Beta) will support Validating parameters, fields and properties

1) Article validate-parameters-using-attributes has implementation of

public class NotEmpty : ParameterAttribute

public class NotNull : ParameterAttribute

[AttributeUsage(AttributeTargets.Parameter)]

public abstract class ParameterAttribute : Attribute

{

public abstract void CheckParameter(ParameterInfo parameter, object value); 

}

It also Required a method attribute with a method boundary aspect to process the parameter attributes.

2) In the comment to the article there are links to very similar implementation for NonNull/NonEmpty    

[return: NonNull] public SomeObject SomeMethod([NonNull] AnotherObject param1)      

The source code is located In google code Torch/DesignByContract

3) another more complicate example is described in http://badecho.com/2011/11/validating-method-parameters-with-postsharp/