About switch case statements...

[Bill Baxter]

On Mon, Nov 16, 2009 at 9:30 AM, KennyTM~ <kennytm at gmail.com> wrote:
> On Nov 17, 09 01:12, Bill Baxter wrote:
>>
>> On Mon, Nov 16, 2009 at 8:24 AM, Andrei Alexandrescu
>> <SeeWebsiteForEmail at erdani.org>  wrote:
>>>
>>> Walter Bright wrote:
>>>>
>>>> Andrei Alexandrescu wrote:
>>>>>
>>>>> I was hoping the lesson learned would be to fix switch as was
>>>>> suggested.
>>>>
>>>> I checked, because it wasn't written in the way I usually write things,
>>>> and sure enough it wasn't code I wrote :-)
>>>>
>>>>  From the changelog for D 0.129: "Incorporated Ben Hinkle's new
>>>> std.format
>>>> which can print general arrays."
>>>>
>>>> http://www.digitalmars.com/d/1.0/changelog1.html#new0129
>>>
>>> So people are liable to make the mistake.
>>>
>>> Andrei
>>>
>>
>> What about when you want to fall through to a multiple label?  Or a range
>> label?
>>
>> case 0:
>>     // do stuff
>>     goto case ??;
>> case 1: .. case 9:
>>      // do more stuff
>>      goto case ??;
>> case 10,20,30:
>>      // still more stuff
>>
>> The obvious answer would seem to be just "pick any one".
>> I just bring it up because I haven't seen that ... uh case ...
>> mentioned by anyone.
>>
>> --bb
>
> Since
>
> case a:
> ..
> case b:
>
> expands to
>
> case a:
> case a+1:
> case a+2:
> // ....
> case b:
>
> and
>
> case a,b,c,d:
>
> expands to
>
> case a:
> case b:
> case c:
> case d:
>
> Your speculation is correct. Please note that the "goto case X;" statement
> works *now*, so there's no need to guess its behavior.

Seriously?  Didn't realize.

So valid end-of-case statements would be:
   break;
   return;
   continue;
   goto *;
   goto case *;
And if you don't have one of those then it's an error?

Could this get into difficult-to-verify territory?  And therefore be
difficult to implement?
It looks like the exact same problem as enforcing that all code paths
return a value, which is something I think D doesn't currently enforce
because it's too hard.   So you run into Walter's dislike for
errors/warnings that are incorrect because the compiler is too stupid.


--bb