Look at the following code snippet. Assigning nullable type to not nullable type C 3. Next Recommended Reading. Windows 10 Vs Windows Visual Studio Vs Visual Studio Understanding Matplotlib With Examples. Understanding Numpy With Examples. C Evolution. Everything That Every. For example:. HasValue property returns false. Beginning with C 7. You always can use the following read-only properties to examine and get a value of a nullable value type variable:. HasValue indicates whether an instance of a nullable value type has a value of its underlying type.
Value gets the value of an underlying type if HasValue is true. The following example uses the HasValue property to test whether the variable contains a value before displaying it:. You can also compare a variable of a nullable value type with null instead of using the HasValue property, as the following example shows:.
If you want to assign a value of a nullable value type to a non-nullable value type variable, you might need to specify the value to be assigned in place of null. Use the null-coalescing operator?? GetValueOrDefault T method for the same purpose :. GetValueOrDefault method. You can also explicitly cast a nullable value type to a non-nullable type, as the following example shows:.
At run time, if the value of a nullable value type is null , the explicit cast throws an InvalidOperationException. A non-nullable value type T is implicitly convertible to the corresponding nullable value type T?
The predefined unary and binary operators or any overloaded operators that are supported by a value type T are also supported by the corresponding nullable value type T? These operators, also known as lifted operators , produce null if one or both operands are null ; otherwise, the operator uses the contained values of its operands to calculate the result.
For the bool? For more information, see the Nullable Boolean logical operators section of the Boolean logical operators article. The following example shows that 10 is. For the inequality operator! If there exists a user-defined conversion between two value types, the same conversion can also be used between the corresponding nullable value types. The null-forgiving operator tells the compiler to ignore that warning.
In combination with Entity Framework Core, the null-forgiving operator is also useful for non-nullable navigation properties in entity classes which are again initialized by the library code:.
For records from the database, Entity Framework Core would initialize the properties anyway by assigning values directly to them. But it can also use the constructor for that when present.
The final and probably most important detail to be aware of is the meaning of non-nullable reference types for properties. Just like non-nullable value types, they result in a non-nullable database column. This means that the Required attribute is not needed anymore.
Instead, the type of the property must be either nullable or non-nullable. Special care must be taken when introducing nullable reference types in an existing codebase. Look at the following property:. After enabling the nullable reference types, the database column will become non-nullable because the same syntax now means a non-nullable type. To keep the same database model, the type should be changed to a nullable reference type:. Fortunately, when generating a new migration, there will be a warning because of the column data type change in case you forget to make this modification in code.
Still, it requires you to pay enough attention and review the generated migration. But you should be doing that anyway. In this article, I looked at the experience of using nullable reference types one year after the initial release. I started with the basics, describing how the functionality works.
I continued with a closer look at the nullable directive as a tool for incremental introduction of nullable reference types into existing code. I explained how class libraries can provide information about nullable reference types to the consuming code and concluded with a closer look at support for nullable reference types in Entity Framework Core.
For new projects, I would recommend you enable the feature and do your best to write code without warnings. This article was technically reviewed by Yacoud Massad. This article has been editorially reviewed by Suprotim Agarwal. C and. Organized around concepts, this Book aims to provide a concise, yet solid foundation in C and. NET, covering C 6. NET Core, with chapters on the latest. NET Standard and C 8. Use these concepts to deepen your existing knowledge of C and.
NET, to have a solid grasp of the latest in C and. NET OR to crack your next. NET Interview. Views: Abstract: In this tutorial, I look at the state of the Nullable Reference Types feature in C , one year after its initial release. Was this article worth reading? Share it with fellow developers too. Damir Arh has many years of experience with software development and maintenance; from complex enterprise software projects to modern consumer-oriented mobile applications.
Although he has worked with a wide spectrum of different languages, his favorite language remains C. In his drive towards better development processes, he is a proponent of Test-driven development, Continuous Integration, and Continuous Deployment. He shares his knowledge by speaking at local user groups and conferences, blogging, and writing articles. He is an awarded Microsoft MVP for. NET since Feedback - Leave us some adulation, criticism and everything in between! Featured Tools.
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