What Does 'null!' Mean in C# Nullable Reference Types?

Exploring the "null!" construct in C#

The C# null! construct is a significant feature introduced with Nullable Reference Types. To understand its purpose, we need to examine the changes in C# 8.0 concerning null safety.

Null Safety Enhancements in C# 8.0

C# 8.0 fundamentally altered how reference types handle nullability. By default, reference types are now non-nullable, meaning they cannot be assigned null values. This crucial change aims to proactively prevent NullReferenceException errors by demanding explicit handling of potential null values within your code.

The ? and ! Operators: Defining Nullability

Two operators govern nullability: ? and !.

• The ? operator designates a variable as nullable, permitting the assignment of null.
• The ! operator asserts that a potentially nullable variable holds a non-null value, effectively bypassing null checks.

Deconstructing null!

null! represents a specific application of the ! operator. Normally, ! is used on a variable to confirm its non-null state. However, applying ! to the null literal creates a seemingly contradictory situation: null declared as non-nullable.

This behavior arises because the null literal is inherently nullable. By using null!, we explicitly override this default nullability, declaring null as a valid assignment for a non-nullable variable. This essentially informs the compiler to accept null in this specific context, even though the variable is declared as non-nullable.

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