C# @ modifier for methods parameters

Question

I was using ReSharper plugin on VS2010 and i was generating an interface method. ReSharper put an @ on the parameter name. WHat is that used for?

int Count(Func<ContratoList, bool> @where); 

Whats the difference for

int Count(Func<ContratoList, bool> where); 

Thanks!

Answer 1

The @ symbol allows you to use reserved words in a variable name.

int @class = 1;  void MyMethod(int @goto);  bool @public { get; set; } 

As Marc correctly pointed out in his comment and his answer, ReSharper is actually wrong to do this because where is a Contextual Keyword and is not actually a reserved word, so your method will compile without the @.

Answer 2

In many ways, resharper is wrong to do this. where is a contextual keyword, meaning: it only acts as a keyword in some very specific scenarios (i.e. LINQ). In the position indicated, it actually does nothing. It would not be confused as a keyword there, as when the C# language designers add keywords to C# they need to ensure pre-existing code continues to compile (as far as possible), and that would have been legal in earlier C#.

The usage of @ also confuses/complicates some tools (razor, in particular, since razor already uses @ to indicate the start of code - meaning that for a variable using @ (i.e. @string) sometimes you need @ and sometimes you need @@ - and I know of at least one false-positive IDE warning this can cause).

However! If the parameter was if or class etc, then @if / @class allows you to use that as a variable name rather than getting confused as a C# keyword. That also isn't a great idea, note. But by the same token, we wouldn't start doing that to all our code (string @name = ... etc) - so why do it here? It isn't needed, and as demonstrated by this question, it has added confusion.

Personally, though, I'd find a parameter name that isn't a keyword or contextual-keyword.