Why Does Visual Studio Suggest Nullable Types for Newly Created Arrays in C#?

Why Does Visual Studio Type a Newly Minted Array as Nullable?

When declaring a new array in C#, Visual Studio may suggest adding the ? operator to indicate that the type might be nullable. This can be surprising, as you would expect a newly instantiated array to always have a non-null value.

Nullable Reference Types

In C# 8.0 and later, nullable reference types became available. This feature allows you to annotate reference types with a ? to indicate that they can be assigned a null value. When enabled, the compiler will check for potential null references and issue warnings or errors accordingly.

Implicit Typing

When using the var keyword to declare a variable, the type is inferred from the initialization expression. If you assign an array to a var variable, it will infer the type as TVal[]?, where TVal is the type of the array elements. This is because var infers nullable reference types for reference types when nullable context is enabled.

Reason for Nullable Arrays

The reason for this behavior is that Visual Studio attempts to be cautious and guard against potential null references. While it is true that a newly minted array is unlikely to be null, it is possible for the array to become null later on, either explicitly (e.g., assigning null to it) or implicitly (e.g., resizing the array to zero length).

Conclusion

Although it is uncommon for a newly minted array to be null, Visual Studio suggests annotating it with the ? operator as a safety measure to prevent potential null reference exceptions later on in the code. If you are certain that the array will never be assigned null, you can safely remove the ? operator.

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