Coalesce vs empty string concatenation

Question

My coworker is new to C# and didn't know about the coalesce operator. So, I saw him write a line of code like this:

string foo = "" + str;

The idea being that if str is null, this expression would return an empty string. Of course, that could be rewritten as this:

string foo = str ?? "";

And I feel that would be more readable. But is it really that big a deal? Are the readability benefits enough to suggest going back and making those lines look like the second? Or is this one of those things that I should learn to let go (provided that my coworker is educated on the best way to do this in the future)?

EDIT: Just a note, I appreciate the efficiency comments, but this isn't really being used in any situations where that performance would be critical. So while that info is interesting, it's not necessarily what I feel is important.

Answer 1

IMO, it is much better to clearly define such logic i.e. don't use string concatenation to avoid null string and use conditional statement or ?? operator.

Regarding other comments:

there is also a performance benefit to using the null-coalescing operator, since no concatenation need take place (and, therefore, no extra string instance is being created unnecessarily)

Not true. C# compiler compiles "" + string2 to the 100% same code as string1 ?? "". Moreover C# compiler translates + operator to call to string.Concat method which in turn checks arguments with string.IsNullOrEmpty function and doesn't allocate a new string in this case.

Also I would recommend the use of String.Empty over "" as it is a constant and does not require the creation of a new String

.NET framework supports string interning so "" and string.Empty point to the same memory region

Answer 2

I don't think one is any more readable than the other personally. I prefer this:

string foo = str ?? "";

simply because I really like the ?? operator.

If you are a brand newbie, I think that this would be a little easier to understand:

string foo = str == null ? "" : str;

or

string foo = "";
if (str != null) foo = str;

However, you kinda need to ask youself, "How simple do you really want to get?"

Answer 3

While I prefer the second line from the technical perspective, the first line is actually more readable to me...