Question

In cases where the full text of the format string is static and known at compile time, shouldn’t a missing format string parameter be a compile-time error or, at the very least, warning?

ReSharper catches this, but it’s just an underlined squiggle. I was under the impression that this would trigger a general compile-time error:

string x = string.Format("soeuotnh {0}");

Is there any way to trigger a warning on this kind of error without having to run my code through FxCop or something? Even C/C++ compilers will trigger an warning/error for such a blatantly clear bug (though they generally won’t check type-safety).

Answer 1

I have filed a request for consideration of this feature on Microsoft Connect, as I feel that

• The answers saying “people would prefer their code compile and fail at runtime if it’s a not very hot codepath” is just absurd and has no place in non-interpreted languages, and especially not explicitly-defined, strongly-typed languages that place such an importance on type safety as C#.
• The answers saying the compiler is physically not capable of (ever) deducing the format string and the parameters array at compile time are also incorrect. Yes, there are times when the compiler cannot deduce one or the other (or both) at compile time, and there’s nothing that can be done about those, but many other times, it has the full info at its disposal.
• The answers saying this is outright not the compiler’s job just because the spec doesn’t mention throwing a warning for this kind of behavior are missing the fact that the spec is the minimum that a compiler should implement, and the compiler is free (and does indeed to a great, great extent) to go above and beyond so long as it’s not in conflict with the spec.
• The answers saying C compilers don’t do this either are plain wrong – I have posted examples otherwise.
• The answers saying the code sample I posted does not throw an exception at runtime are blatantly wrong (though most have been edited since then).

At the end of the day, it’s a “yes it could, no it doesn’t, maybe it should” situation. I was trying to make sure that there wasn’t something I could set in the compiler (not third party software) to make it more agressive with its warnings or if there were some way I could change my code to make it throw an exception (for instance, declaring everything as const), but it turns out (thus far) that that is not possible. Regardless of the response of the Visual Studio team on the issue I opened on MS Connect, the fact remains that the compiler certainly can catch a great many string formatting exceptions at compile time, that it would be a benefit… but it remains for the VS team to determine whether or not it is something worth implementing.