Chad J wrote:
Don wrote:
Things like
case A:
case B:
foo();
break;
do not involve fallthrough bugs. If there's a bug in that code at all,
it's that case A doesn't do anything. Empty case statements are not
bug-prone.
My intent is not to forbid these. I suppose I've tried to damage them
as little as possible Letting them slip through without notation would
do better on that count. It's a trade-off between that and easier
(general) fallthrough syntax.
If you think general fallthrough syntax is important, you've
misunderstood the argument for this feature. See below.
With this syntax the code required to convert C-style switch-case to
D-style becomes much easier. You can just look for case and replace :
with !:. Otherwise you have to figure out where to put the goto case
statement, which is usually easy enough for a human, but can be tricky
for a program that doesn't have a D parser. Unless you are OK with
generating some garbage:
I think you've just created the strongest argument AGAINST this feature:
that it makes it too hard for machine-generated code. Forget the !:
hack. No chance.
The thing is, that with the "goto case" syntax, D already has support
for explicit fallthrough. No new syntax is required.
I know this. Walter knows this. Why hasn't it been given emphatic
thumbs up?
I suspect it's because he's either busy with more important things or
really enjoys fallthrough.
He made it very, very clear that he thinks that legitimate fallthrough
is common. If he's right, then this whole thing is a bad idea.
With something like this, you're really wasting your time making a patch
for it. Patches are only worthwhile in the cases where Walter hasn't
said anything, or in which he made a positive comment but nothing has
happened for a long time. Once he's said something negative about a
feature, providing a patch is not going to change his mind.
BTW, it's _really_ difficult to get an unsolicited patch into DMD. It's
happened about twice ever.
Given how easy it is to remove implicit fallthrough and given that he's
expressed a strong fondness of the fallthrough behavior, I suspect it's
more the latter than the former.
At any rate, I've decided to solve both. So here's a patch to make it
even easier to enact (especially docs + lib migration), and also a
syntax to keep fallthrough easy and compact where desired.
If the syntax is a bad idea, then it can be ditched, and I'll make a new
patch. All Walter has to do is say the word.
The argument for it comes down to this: "fallthrough is very rare and
therefore, most uses of fallthrough are bugs". If many modifications to
(say) Phobos are required, then the argument for this feature is false.
From a comment someone made previously, there were about three
instances of it in Phobos. If you found you needed to make many changes
than that, I'll switch sides to Walter's camp. But I think you've just
gone about this wrong way. Although, the "auto-generated code" argument
would now need to be addressed.
