Method Returns string[] But var types as string[]?

[MelbourneDeveloper]

Version Used:

See below

Steps to Reproduce:

1. Clone this repo https://github.com/MelbourneDeveloper/Urls @ 0497258a6f99e78af43b50c9bacb8ec926019bce
2. Open in Visual Studio
3. Open this code and hover over tokens

UrlExtensions -> ToRelativeUrl

Expected Behavior:

tokens should be string[]

Actual Behavior:

tokens is string[]?

Visual Studio Info:

Microsoft Visual Studio Professional 2019
Version 16.9.2
VisualStudio.16.Release/16.9.2+31112.23
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Version 4.8.04084

Installed Version: Professional

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[Youssef1313]

The current compiler behavior is expected. See the note at var - C# reference:

When var is used with nullable reference types enabled, it always implies a nullable reference type even if the expression type isn't nullable.

See also LDM-2019-12-18.

Note that the compiler correctly tracks the state of the variable, i.e, it won't show a warning when you dereference it, unless you assign it a nullable value later on.

[MelbourneDeveloper]

@Youssef1313 Thanks but...

I guess a why is in order?

[MelbourneDeveloper]

Can I take it from the link above that the intention is to change the behavior in future?

If that's the case, won't a lot of existing code be changed?

[Youssef1313]

Can I take it from the link above that the intention is to change the behavior in future?

Nope, The conclusion of the LDM is that var? is not needed (var is effectively what var? was suggested to do).

Note that you won't get a warning if you don't assign it a nullable value.

See SharpLab for an example.

[MelbourneDeveloper]

@Youssef1313 but this is the problem, and the reason why I didn't end up just specifying string[] in the first place:

Perhaps this code rule needs adjusting for this scenario.

IDE0007

[MelbourneDeveloper]

Friends don't let friends violate code rules

[MelbourneDeveloper]

If I want to avoid this issue I have to disable warnings everywhere

[MelbourneDeveloper]

This is particularly nasty:

[Youssef1313]

For your scenario, I think you can use var safely. The compiler will know that Split doesn't return null, and won't warn. This satisfies both IDE0007 and the compiler.

[MelbourneDeveloper]

@Youssef1313 not gonna pretend that I completely understand why var creates a nullable type, but I can say with certainty that I expected it not to, and I expect that most other people will as well.

[MelbourneDeveloper]

For your scenario, I think you can use var safely. The compiler will know that Split doesn't return null, and won't warn. This satisfies both IDE0007 and the compiler.

@Youssef1313 Look above. It doesn't.

[MelbourneDeveloper]

Or, to put it another way...

I can't use var in this scenario because the quick info results are too confusing. So, I need to specify the type explicitly so it's clear what is going on.

If IDE0007 didn't kick in, in this case, it would be nice.

[Youssef1313]

I mean, yes var will change the type to string[]?. But it's not a problem for such a case (to me at least).

To be explicit about tokens being string[], I think IDE0007 needs to be adjusted for that.

Tagging @CyrusNajmabadi @sharwell for thoughts about IDE0007. I tend to agree that IDE0007 could be relaxed not to warn if the nullable annotation is different.