Question

I have the following:

MyEnum? maybeValue = GetValueOrNull();

if (null != maybeValue)
{
    MyEnum value = (MyEnum)maybeValue;
}

What I want to know is if that explicit (MyEnum) cast is necessary on an instance of type MyEnum?. This seems like a simple question, I just felt paranoid that there could possibly be some runtime error if I just did MyEnum value = maybeValue within that if statement.

Answer 1

A number of answers have noted that using the Value property avoids the cast. This is correct and it answers the question:

is that explicit (MyEnum) cast necessary on an instance of type “MyEnum?” ?

However, we haven’t addressed the other concern:

I just felt paranoid that there could possibly be some runtime error if I just did MyEnum value = maybeValue within that if statement.

Well, first off, you cannot simply assign a nullable value to a variable of its underlying type. You have to do something to do the conversion explicitly.

However, if you do so in the manner you describe — checking whether there is a value first — then this is safe. (Provided of course that no one is mutating the variable containing the nullable value between the call to HasValue and the fetch of the value.)

If you use ILDASM or some other tool to examine the generated code you will discover that casting a nullable value to its underlying type is simply generated as an access to the Value property; using the cast operator or accessing the Value property is a difference which actually makes no difference at all. The Value property accessor will throw if HasValue is false.

Use whichever syntax you feel looks better. I personally would probably choose the “Value” syntax over the cast syntax because I think it reads better to say “if it has a value, gimme the value” than “if it has a value, convert it to its underlying type”.