C# object vs. object? (nullable object)

Question

Short question - what is difference between object and object? (nullable object)?

I know what nullable types are and for example with numbers it makes perfect sense, but what is the point of nullable object, when object by itself can be null. Am I missing something?

Story behind. I had project in Core 5.0 and 3.1, both had background tasks and based on Microsoft doc, I had function with object parameter like this:

private void DoWork(object state)
{
   //some code
}

Example from Microsoft documentation - Core 5.0

But in Core 6.0 there are some changes and now it looks like this:

private void DoWork(object? state)
{
   //some code
}

Example from Microsoft documentation - Core 6.0

Which now triggers Warning CS8632: The annotation for nullable reference types should only be used in code within a '#nullable' annotations context.

It is not much of a issue, but more like a curiosity. Thanks in advance.

So you're essentially asking "what is the point of nullable reference types?" — ProgrammingLlama
– ProgrammingLlama, Commented May 18, 2022 at 9:57
This is a new feature called nullable reference types. There is little overlap with Nullable for value types, although it uses the same syntax. — Jeroen Mostert
– Jeroen Mostert, Commented May 18, 2022 at 9:57
NullReferenceException is something that has cost billions. This is a method of forcing the software developer to reduce this problem by explicitly marking an reference type to be able to contain a null value. The compiler can also get more insight into which reference is able to contain a null value and point this out to the developer. — Jeroen van Langen
– Jeroen van Langen, Commented May 18, 2022 at 10:04
Ahhh I see. I am dum dum, if only I would read that warning more carefully, then google would not always showing me this link nullable value types and I would find that doc page You sent. Now it is obvious. Thanks a lot guys. If You post it as answer, I will mark it ;) — Martin
– Martin, Commented May 18, 2022 at 10:48

thisisnabi · Accepted Answer · 2022-05-18 11:08:17Z

2

First: T? is syntax sugar for the Nullable<T>

Microsoft added this pattern in .Net Core 6 for all owned libraries, so you can doing this.
I'ts just to warn you that there may be null in here.

when you add <Nullable>enable</Nullable> tag to project file, enable this ability of compiler.

edited May 18, 2022 at 11:08

answered May 18, 2022 at 10:42

thisisnabi

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