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Date: Wed, 06 Aug 2014 13:40:16 +0100
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Subject: Re: [PHP-DEV] [RFC] Disallow multiple default blocks in a single
 switch statement
From: rowan.collins@gmail.com (Rowan Collins)

Lester Caine wrote (on 06/08/2014):
> On 06/08/14 11:16, Rowan Collins wrote:
>> According to the bug report, HHVM also accepts multiple default blocks,
>> but uses the first rather than the last. It's probably not worth
>> implementing specific code there to take the last default label just in
>> order to adhere to a 5.6 spec, but is worth making it detect multiple
>> labels to bring it in line with the proposed change.
>>
>> So either we declare the php.net implementation to be in violation of
>> the spec (which isn't completely insane - the spec shouldn't mirror
>> behaviour to the point of incorporating the entire bug list); or we
>> document the php.net behaviour as "correct", but accept that nobody is
>> going to implement that part of the spec as written, and fix it in the
>> next release of both the implementation and the spec.
> It is perhaps interesting that this problem has not turned up before? As
> I indicated in another thread I was surprised to see 'default' as the
> first item in an example. I'm sure I'm not alone in always putting it at
> the end, and I quite often will have a previous block which does not
> have a 'break' so that the default element is added to other actions on
> some keys for that reason. How much of the core PHP is still 'normal
> practice' rather than 'by design' :)
>

You could equally have the default case run some extra logic *before* 
one of the steps, since it doesn't have to be last. The goto-like 
behaviour of case and default labels originates in C, which makes this 
answer on SO worth mentioning: http://stackoverflow.com/a/3110478/157957

The reason some languages require default to be the last label is 
presumably that they treat it as equivalent to a case statement that 
always matches, and so never test lower labels.

"Normal practice" is often stricter than what is technically possible in 
a language, because it is aimed at writing readable and maintainable code.

Which in turn has no bearing on the ability to specify multiple defaults 
(which never makes sense, except as a result of a lazy code generator).
-- 
Rowan Collins
[IMSoP]