CODEWITHSUNDEEP
c#c#-8.0nullable-reference-types
Triazic
Triazic

Reputation: 53

I want to warn the compiler about possible nulls from external code

In the below, C# is confident that 'property' will never be null, but I KNOW that it can be, because the external library is not produced with C#8/nullable types:

#nullable enable
SomeExternalClass obj = GetSomeExternalObjectFromAnOldAPI();
SomeExternalProperty property = obj.SomeProperty;
DoStuff(property); // C# is confident that property is not null, here

Here is a screenshot of the condition:

Failure 1

Doing the following doesn't provide a null warning either. C# still confidently assumes the external API is perfectly non-nullable:

#nullable enable
SomeExternalClass obj = GetSomeExternalObjectFromAnOldAPI();
SomeExternalProperty? property = obj.SomeProperty;
DoStuff(property); // C# is still confident that property is not null, here

Failure 2

Is there a way that I can force C# to acknowledge that a variable may be null, even if it is supposedly confident it won't be? The opposite of the ! symbol. 'Trust me, this garbage can be null..'

RESOLVED. ACCEPTED ANSWER:

#nullable enable
SomeExternalClass obj = GetSomeExternalObjectFromAnOldAPI();
SomeExternalProperty? property = obj.SomeProperty ?? null;
DoStuff(property); // C# is now warning about possible null

Upvotes: 5

Views: 815

Answers (2)

Julien Couvreur
Julien Couvreur

Reputation: 4983

You can write a method ‘void MaybeNull([System.Diagnostics.CodeAnalysis.MaybeNull] T t)’ and use it.

Upvotes: 0

user544141
user544141

Reputation: 90

Try:

ElementId? viewTemplateId = (revitView.ViewTemplateId ?? someNullTypeOfYourChoosing);

Alternatively, allow the View and revitView.ViewTemplateId structs to be nullable/return nullable types.

Upvotes: 1

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