Nullable value types and switch expression

[Dersei]

I was playing with C# 8.0 in Visual Studio 2019 Preview and when I was testing switch expression I wrote something similar to this

int? test = 0;
bool? tested = test switch
{
    0 => false,
    1 => true,
     null => null,
     _ => null
};

This results in error
CS0037 Cannot convert null to 'bool' because it is a non-nullable value type

It's easy to fix by casting any of result values to bool?, however I would like to know if there is any reason why this works in this way?

[YairHalberstadt]

expressions in C# are almost never target typed, so declaring tested as a bool? makes no difference to the type of the switch.

There are various proposals to improve this behaviour for the conditional operator. The same proposals could probably be applied here.

[ufcpp]

The same proposals could probably be applied here.

#450.

[DavidArno]

This issue is now covered by the championed proposal, #2389, and so can be closed.

[Thaina]

@DavidArno Not sure that #2389 already covered nullable. It seem only mention the base type

[yaakov-h]

#2389 covers the target type, which is the exact case of the OP.

I wish it could cover nullable without target-typing (e.g. var tested = ...), but that's not quite the use case here.

[DavidArno]

@yaakov-h,

I'd assume #2389 should cover var tested = …, because it shouldn't be looking at the type of tested to determine the type of the expression. My assumption was that it would take the common type for true, false and null, which is bool?. I'll add something to that issue to seek clarification on this point.

[DavidArno]

@yaakov-h, so you were right. #2389 wouldn't work for var tested = …, so I've lost interest in it.

[gafter]

This would be fixed by either #2389 or #33. It is likely that one or both of these will be included in C# 8.