Not null parameter c#

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These provide more detail about the characteristics of your API. This additional information helps callers use your API correctly.

Remember you specify preconditions using the following attributes:. You've likely written a method like this to return null when the name sought wasn't found. The null clearly indicates that the record wasn't found. In this example, you'd likely change the return type from Customer to Customer? Declaring the return value as a nullable reference type specifies the intent of this API clearly:.

For reasons covered under Generics nullability that technique may not produce the static analysis that matches your API. You may have a generic method that follows a similar pattern:. The method returns null when the sought item isn't found.

You can clarify that the method returns null when an item isn't found by adding the MaybeNull annotation to the method return:. The preceding code informs callers that the return value may actually be null. It also informs the compiler that the method may return a null expression even though the type is non-nullable.

When you have a generic method that returns an instance of its type parameter, T , you can express that it never returns null by using the NotNull attribute. You can also specify that a return value or an argument isn't null even though the type is a nullable reference type.

The following method is a helper method that throws if its first argument is null :. After enabling null reference types, you want to ensure that the preceding code compiles without warnings.

When the method returns, the value parameter is guaranteed to be not null. However, it's acceptable to call ThrowWhenNull with a null reference. You can make value a nullable reference type, and add the NotNull post-condition to the parameter declaration:. The preceding code expresses the existing contract clearly: Callers can pass a variable with the null value, but the argument is guaranteed to never be null if the method returns without throwing an exception.

You're likely familiar with the string method String. IsNullOrEmpty String. This method returns true when the argument is null or an empty string. It's a form of null-check: Callers don't need to null-check the argument if the method returns false. To make a method like this nullable aware, you'd set the argument to a nullable reference type, and add the NotNullWhen attribute:. That informs the compiler that any code where the return value is false doesn't need null checks.

The addition of the attribute informs the compiler's static analysis that IsNullOrEmpty performs the necessary null check: when it returns false , the argument isn't null. The String. IsNullOrEmpty String method will be annotated as shown above for. NET Core 3. You may have similar methods in your codebase that check the state of objects for null values. The compiler won't recognize custom null check methods, and you'll need to add the annotations yourself. When you add the attribute, the compiler's static analysis knows when the tested variable has been null checked.

The postconditions for ref and out arguments are communicated through the return value. Consider this method shown earlier in a nullable disabled context :.

The preceding method follows a typical. NET idiom: the return value indicates if message was set to the found value or, if no message is found, to the default value. If the method returns true , the value of message isn't null; otherwise, the method sets message to null. Throughout the process of developing these, I have been learning programming paradigms, concepts, and techniques that help me evolve professionally by the day.

My passion for both quality-code and open-source urges me to share my knowledge with the. NET world. Primitive data types before C 8 can only accept null values with several syntactic devices. As you see, the compiler is worried only about the integer null , which cannot bear a null value. It shows no worries whatsoever about the PassNull method. Yes, the compiler is friendly, but we pay dearly for it, as we see.

This is among the reasons Microsoft made this huge change within the reference types. For one thing, be prepared to react to tons of warnings. The feature is disabled by default, and you need to manually turn it on. Open your project file to see how you do it:. Your C version should be at least 8. You need to enable the global reference types to be Nullable.

I personally have set Treat Warnings As Errors to true, since this provides more visual information about what goes on in the code. Now, see why this change is called breaking:. Now the compiler is concerned a lot more — hugely to our benefit. Now to the PassNull method — you may have noticed that the compiler does not warn you at the definition of the method, but does not allow you to pass a null value when you invoke it.

If you try to solve this by adding the Null-Conditional Operator to the reference-type parameter at the method definition, the compiler warns you about something else:. Look at this:. You do have the Null-Conditional Operator and you have several more techniques. How fix it? Add the Elvis operator after each variable :. You will not receive anything more than compile-time errors. What you gain with the Non-Nullable Reference types — you protect yourself from bugs, which lead to Null Reference exceptions.

Do Nothing The final option is to simply do nothing. Furthermore, only a small amount of code is needed for the null check in any given function. Author Contacted. This content is in the. NET topic. Related Editorial. Related Sponsor Stuck trying to diagnose connectivity or performance issues? Getting Started with gRPC and. Microservices — the Letter and the Spirit.

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Learn more. Ask Question. Asked 13 years, 2 months ago. Active 2 years, 4 months ago. Viewed 78k times. Currently I write something like Neil C. Obremski Neil C.

Obremski With recent versions of C , using "nameof " works better: throw new ArgumentNullException nameof arg ; That way, if you refactor the name, if ripples into your throw statement — Flydog C 8 now supports nullable reference types which is a compiler option you can turn on in your project. Add a comment. Active Oldest Votes. There's nothing available at compile-time, unfortunately. Jon Skeet Jon Skeet 1. I would also like to see compile-time errors being raised.

I admit it may seem perverse, but it does compile Trias: Yes, in that incredibly obscure edge case, combined with there being a typo, combined with a lack of tests around that code, you'd end up with a problem. By that point I think you have bigger problems though : — Jon Skeet.

Jon: Granted.