Empty String Literal

Question

I have come across some code during a code-review where a old coworker has done the following:

const string replacement = @""; 

This string is used in a regex expression as a replacement for what is matched. My question is what is the purpose of adding the @ literal sign to the beginning of an empty string. There should not be anything to literally interpret.

Would there be any difference in impact between: @""; and "";?

Answer 1

This string is used in a regex expression

Regular expressions make heavy use of the \ character. For example, the following is a regular expression to match precentages from 0 to 100 that always have four decimal places:

^(100\.0000|[1-9]?\d\.\d{4})$

Because \ has to be escaped in the more common C# syntax to \\ the @"" form allows for the regex to be more easily read, compare:

"^(100\\.0000|[1-9]?\\d\\.\\d{4})$"
@"^(100\.0000|[1-9]?\d\.\d{4})$"

And for this reason people often get into the habit of using the @"" form when they are using regular expressions, even in cases where it makes no difference. For one thing, if they later change to something where it does make a difference the only need to change the expression, not the code for the string itself.

I would suggest that this is likely why your colleague used @"" rather than "" in this particular case. The .NET produced is the same, but they are used to using @"" with regular expressions.