C#: Workaround for Illegal Switch Statement?

Question

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Switch statement fallthrough in C#?

The following code is illegal in C# because control cannot fall through from one case label to another. However, this behaviour is perfectly legal in C++. So, how would you go about coding the same behaviour in C#?

enum TotalWords
{
   One = 1,
   Two,
   Three,
   Four
}

public String SomeMethod(TotalWords totalWords)
{     
     String phrase = "";

     switch (totalWords)
     {
        case TotalWords.Four:
             phrase = "Fox" + phrase;
        case TotalWords.Three:
             phrase = "Brown" + phrase;
        case TotalWords.Two:
             phrase = "Quick" + phrase;
        case TotalWords.One:
             phrase = "The" + phrase;
             break;

        default:
             break;
     }

     return phrase;
}

Duplicate of http://stackoverflow.com/questions/174155/ which includes a good answer using "goto case". — Michael Stum, Jan 07 '10 at 02:40

score 4 · Accepted Answer · edited May 20 '14 at 17:37

Eric Lippert, who works on the language, talks about it here:
http://ericlippert.com/2009/08/13/four-switch-oddities/

Short version: the easiest fix is to use a goto:

switch (totalWords)
 {
    case TotalWords.Four:
         phrase = "Fox" + phrase;
         goto case TotalWords.Three;
    case TotalWords.Three:
         phrase = "Brown" + phrase;
         goto case TotalWords.Two;
    case TotalWords.Two:
         phrase = "Quick" + phrase;
         goto case TotalWords.One;
    case TotalWords.One:
         phrase = "The" + phrase;
         break;

    default:
         break;
 }

I think the rationale here is that 9 times out of 10 a missing break is a bug rather than intentional. Forcing you to use break and an explicit branch helps keep you from writing bugs and makes it clear to future maintainters that the fall-through is intentional.

"I think the rationale here is that 9 times out of 10 a missing break is a bug rather than intentional." - which is exactly why they should have never required it in the first place. — BlueRaja - Danny Pflughoeft, Jan 07 '10 at 03:16
So you think switch shouldn't need the `break;` and just do it automatically at label boundaries? That's how VB does it. — Joel Coehoorn, Jan 07 '10 at 03:41

score 0 · Answer 2 · answered Jan 07 '10 at 02:48

Given that this is a numeric enumeration, and you're doing essentially the same operation in all cases, you can re-write it as a loop:

String[] phrase_bits = new String[] { "The", "Quick", "Brown", "Fox" };

public String SomeMethod(TotalWords totalWords)
{
    int x = (int) totalWords;
    String phrase = ""
    while (--x >= 0) {
        phrase = phrase_bits[x] + phrase
    }
    return phrase
}

This is not a generic answer for all switch statements, but for this case it's fairly nice.

It assumes that TotalWords is linear though, which it is in this case, but if it would be i.e. a flag (1,2,4,8), it would fail. — Michael Stum, Jan 07 '10 at 02:53

C#: Workaround for Illegal Switch Statement?

2 Answers2