Why does this superfluous comma compile?

Question

In looking through some legacy code, I came across this enum:

    public enum cmdResults 
    {
        cmdNotFound = 0,    
        cmdFound    = 1,    
        cmdExit     = 2,    
        cmdSuccess  = 3,    
        cmdFail     = 4,    
        cmdTimeout  = 5,    
        cmdProcess  = 6,
        cmdAddTime  = 7,
    };

On noting the comma following the final enum member, I was stunned; I removed it, and, as expected, it still compiled. But why does it work with that final comma?

(And that's not mentioning the strange-to-me ordering of members; I would either put a new "cmdNothing" at index 0, or at least have "cmdFail" take that spot)

The ordering could be explained by the enum values growing over time. New values can't replace existing ones otherwise any code calling this - the enum is public after all - would break. — ChrisF, Mar 19 '13 at 20:55

score 11 · Accepted Answer · answered Mar 19 '13 at 20:55

11

Because the C# compiler writers choose to make an optional comma at the end a valid syntax.

I very much like this, as it means you don't need to special case the last line. You can copy-paste lines around, add new lines at any position (including the end) without thinking about where it is, remove lines without needing to fix commas, etc. There is no ambiguity or other problems introduced by allowing the superfluous comma.

answered Mar 19 '13 at 20:55

Servy

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And I, for one, am so pleased that it does allow that...makes adding/removing enum values during quick change/build/test cycles SO much nicer! – JerKimball Mar 19 '13 at 20:58
Note that the same syntax applies to array and object initializers. I also like this very much, especially since it doesn't clutter the version control diffs with unnecessary line changes. – Aasmund Eldhuset Mar 19 '13 at 21:03
To me, it looks 9X uglier than a bag of butts. – B. Clay Shannon-B. Crow Raven Mar 19 '13 at 21:21
2

Apparently you can't please everyone. – Eric Lippert Mar 19 '13 at 22:22
3

@ClayShannon Good thing it's optional and you don't need to use it if you feel that way. – Servy Mar 20 '13 at 13:57

score 3 · Answer 2 · answered Mar 19 '13 at 20:55

3

It compiles because it's legal syntax.

answered Mar 19 '13 at 20:55

Sam I am says Reinstate Monica

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Why does this superfluous comma compile?

2 Answers2