Analyze nullable return value statically?

[Cyl18]

Consider this code:

public static object? ToObject<T>(this T obj) => obj;

Is it possible to analyze whether the return value is nullable by the caller?

string obj1 = "";
var obj1Result = obj1.ToObject(); // should be object

string obj2 = null;
var obj2Result = obj2.ToObject(); // should be object?

In Kotlin, we have code contract like this:

(sorry for my bad grammar

[PathogenDavid]

I believe what you're looking for is the nullable analysis attributes.

Specifically, NotNullIfNotNull: (Full example on SharpLab here)

[return: NotNullIfNotNull("obj")]
public static object? ToObject<T>(this T obj) => obj;

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As an aside:

var obj1Result = obj1.ToObject(); // should be object

With var this will always be object?, but the compiler will know it is not null. (Whether a particular variable is known to be null or able to be null are separate concepts. var is always nullable, but may or may not be known to be null.)

[Cyl18]

thanks!

[PathogenDavid]

No problem, happy new year!