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Date: Wed, 13 Aug 2014 16:38:41 +0200
Message-ID: <CAH-PCH6D=VG51kotk0Edr9YFDn6RBMAOgMMqmd59xxhxz50cGA@mail.gmail.com>
To: Rowan Collins <rowan.collins@gmail.com>
Cc: PHP Internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=001a11343e1e929151050083bec4
Subject: Re: [PHP-DEV] [RFC] Disallow multiple default blocks in a single
 switch statement
From: tyra3l@gmail.com (Ferenc Kovacs)

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On Wed, Aug 13, 2014 at 3:55 PM, Rowan Collins <rowan.collins@gmail.com>
wrote:

> Ferenc Kovacs wrote (on 13/08/2014):
>
>> I think you misunderstood that part, I was thinking about a state machin=
e
>> like this:
>>
>>  1. function doStuff(){
>>  2. switch($state){
>>  3. case OPENDOOR:
>>  4. if(!opendoor()){
>>  5. break;
>>  6.       }
>>  7.     $state =3D SITDOWN;
>>  8. case SITDOWN:
>>  9. if(!sitdown()){
>> 10. break;
>> 11.       }
>> 12.     $state =3D SIPWHISKEY;
>> 13. case SIPWHISKEY:
>> 14.       sipwhiskey();
>> 15.   }
>> 16. }
>>
>>
>>
>> where you modify the switch variable in one case and fall through into
>> another.
>> as I mentioned I don't have a reasonable use-case for multiple defaults,
>> but I can see some for multiple case labels in general, and I don't thin=
k
>> that it is better to have different behavior for case and default in thi=
s
>> regard.
>>
>
>
> The assignments to $state in that code do not make any difference to
> execution, control simply flows forwards whenever there is no "break".
>
> $state is only tested once, to select the initial label to jump to, so no
> amount of reassigning it, or adding duplicate labels, can ever cause a
> second jump.
>
> I'm tempted to write a PHP script that emulates the switch execution by
> building a set of if and goto statements, which might make some of this
> behaviour clearer (not just for this discussion, but for other confusion
> I've seen elsewhere), but I don't have time right now.
>

yeah, and that is a documented behavior, I've just had a momentary
brain-fart here (which is funny considering that at one point I even wrote
a codesniffer rule for generating warnings for fall-through case statements
without an explicit comment).
thanks again for pointing that out. and sorry for the noise.

ps: I still hold onto my no vote, even thought it is a small BC break, it
is still a BC break, I wouldn't consider the current patch as a bugfix(and
even thought that the spec documented this as not a valid syntax hhvm still
supported it, ableit picking the first default when there are more than
one) , I would prefer having it E_DEPRECATED first in 5.next and we can
remove it in 7.0.


--=20
Ferenc Kov=C3=A1cs
@Tyr43l - http://tyrael.hu

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