Question

According to MSDN:

The ?? operator is called the null-coalescing operator and is used to
define a default value for nullable value types or reference types.

But when I run the code below:

Guid test;
Guid otherGuid = test ?? Guid.NewGuid();

I get the error:

Operator ‘??’ cannot be applied to operands of type ‘System.Guid’ and
‘System.Guid’

I thought Guid was a reference type. Is that not the case? Could someone explain to my why this does not work?

Answer 1

Guid is not a reference type, its a value type, you can’t assign it null and that is why you can’t check it with ??

Following line will give you error.

Cannot convert null to ‘System.Guid’ because it is a non-nullable
value type

Guid test = null;

You may use Nullable

Nullable<Guid> test = null;
Guid otherGuid = test ?? Guid.NewGuid();

Or short form

Guid? test = null;
Guid otherGuid = test ?? Guid.NewGuid();