Use an ! operator to assert that a variable is not null.

[ekolis]

This would be useful to simplify conversion of nullable types to non-nullable types:

int? answer = 42;
int magic = answer!; // equivalent to answer.Value or (int)answer

[333fred]

We considered something like this for the initial version of C# 8: #1865. We decided against this, and at this point this would be a breaking change.

[ronnygunawan]

Breaking change can be avoided by introducing a new !! operator.

string? s = null;
string t = s!!; // throws NullReferenceException

[333fred]

@ronnygunawan yes, but note that your example uses reference types and the issue is about nullable value types.

[ekolis]

@333fred I was actually talking about both reference types and nullable value types; sorry if I wasn't clear!

[ronnygunawan]

For nullable value type:

int? i = null;
int j = i!!; // equivalent to i!.Value, throws InvalidOperationException: Nullable object must have a value.

[MatisseHack]

This feature would make using nullables so much cleaner and easier. I run into issues whenever I'm dealing with deserialized data. The models' types are all nullable and I end up having to litter my code with explicit null checks. I've taken to adding the following two extension methods to all my projects to make it slightly cleaner:

public static T GetValue<T>(this T? possibleNull, [CallerLineNumber] int sourceLineNumber = 0) where T : class =>
    possibleNull ?? throw new NullReferenceException($"Value is null on line {sourceLineNumber}");

public static T GetValue<T>(this T? possibleNull, [CallerLineNumber] int sourceLineNumber = 0) where T : struct =>
    possibleNull ?? throw new NullReferenceException($"Value is null on line {sourceLineNumber}");

The new CallerArgumentExpression proposal would improve the exception message, but this is better than nothing. I would love to have a language feature to do this assertion more concisely!

[YairHalberstadt]

Closing as the feature as suggested here is a breaking change