Cannot assign null to an implicitly-typed variable

Question

According to Visual Studio this is not ok:

var foo = null;

But this is ok:

var foo = false ? (double?)null : null;
<         


        

Answer 1

Implicitly typed variable declaration/assignment serves two purposes:

• Decides the value of the variable, and
• Decides the type of the variable.

Your first declaration has null for the value, with no way to figure out the type (it could be anything derived from System.Object, or a Nullable). That is why it is an error.

Your second declaration pinpoints the type as Nullable because of the cast. That is why C# allows it.

It goes without saying that double? foo = null would be much easier to read.