[Issue 199] Label causes scope to collapse into parent

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=199



--- Comment #31 from Stewart Gordon <smjg at iname.com> 2013-05-30 16:13:24 PDT ---
(In reply to comment #29)
> I didn't advocate banning it. I advocate permanent deprecation, 
> because the semantics are bug prone, and we should (arguably) never 
> risk *silently* breaking working code.

Your worry about this is out of all proportion, when you consider that:

(a) All the examples that have so far been posted here are contrived.  Somebody
please show me some real-world code that only works as the programmer intended
because of this "feature".  Surely there's far more real-world code that
_doesn't_ behave as the programmer intended because of this.

(b) D isn't even an ISO (or ANSI or whatever) standard yet.  As such, it's
still a _good_ time to get all the potentially breaking changes out of the way.

(c) D has in its time had some breaking changes that are much more serious than
this.

(d) Even long-standardised programming languages have had breaking changes in
their time.  C has had at least one breaking change in its time, though I don't
know when this came in relation to its standardisation.  C++11 introduces a
change to how template instantiations are lexed, which can cause code to behave
differently.

> There is no reason to remove it for a long time,
> possibly never.
> 
>> The (imo correct) path is that the NoScopeStatment should still 
>> provide no scope, but emit a deprecated message if anything 
>> declared in the scope is used.

If you're going to go as far as that, why not emit a deprecation message if any
declarations appear in it at all?

>> EG:
>> 
>> void main()
>> {
>>     label:
>>     {
>>         int i;
>>     }
>>     writeln(i); //(1)
>> }
>> 
>> (1) should emit a deprecation message.
> 
> Sounds good. Can it be implemented easily?

I can see that it would be complicated to get it right.  The tiny risk of
silently breaking any real-world code doesn't seem to justify it.  As such,
IMM, just fixing this issue and being done with it is the way to go.

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