Why is String.Format static? [closed]

Answer 1

.NET Strings are Immutable

Therefore having an instance method makes absolutely no sense.

String foo = new String();

foo.Format("test {0}",1); // Makes it look like foo should be modified by the Format method. 

string newFoo = String.Format(foo, 1); // Indicates that a new string will be returned, and foo will be unaltered.

Answer 2

I don't actually know the answer but I suspect that it has something to do with the aspect of invoking methods on string literals directly.

If I recall correctly (I didn't actually verify this because I don't have an old IDE handy), early versions of the C# IDE had trouble detecting method calls against string literals in IntelliSense, and that has a big impact on the discoverability of the API. If that was the case, typing the following wouldn't give you any help:

"{0}".Format(12);

If you were forced to type

new String("{0}").Format(12);

It would be clear that there was no advantage to making the Format method an instance method rather than a static method.

The .NET libraries were designed by a lot of the same people that gave us MFC, and the String class in particular bears a strong resemblance to the CString class in MFC. MFC does have an instance Format method (that uses printf style formatting codes rather than the curly-brace style of .NET) which is painful because there's no such thing as a CString literal. So in a MFC codebase that I worked on I see a lot of this:

CString csTemp = "";
csTemp.Format("Some string: %s", szFoo);

which is painful. (I'm not saying that the code above is a great way to do things even in MFC, but that does seem to be the way that most of the developers on the project learned how to use CString::Format). Coming from that heritage, I can imagine that the API designers were trying to avoid that sort of situation again.

Answer 3

I think it is because Format doesn't take a string per se, but a "format string". Most strings are equal to things like "Bob Smith" or "1010 Main St" or what have you and not to "Hello {0}", generally you only put those format strings in when you are trying to use a template to create another string, like a factory method, and therefore it lends it self to a static method.

Answer 4

A big design goal for C# was to make the transition from C/C++ to it as easy as possible. Using dot syntax on a string literal would look very strange to someone with only a C/C++ background, and formatting strings is something a developer will likely do on day one with the language. So I believe they made it static to make it closer to familiar territory.

Answer 5

Because the Format method has nothing to do with a string's current value. The value of the string isn't used. It takes a string and returns one.

Answer 6

Maybe the .NET designers did it this way because JAVA did it this way...

Embrace and extend. :)

See: http://discuss.techinterview.org/default.asp?joel.3.349728.40