Are these two lines the same, '? … :' vs '??'?

Question

Is there a difference between these two lines?

MyName = (s.MyName == null) ? string.Empty : s.MyName

or

MyName = s.MyName ?? st         


        

Answer 1

The only difference is whether you evaluate s.MyName twice or once. The first will do it twice in the case that s.MyName is not null, the second will only ever evaluate it once.

In most cases, this difference doesn't matter, and I'd go with the second because it's more clear and concise.