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Re: @else in Media Queries

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Mon, 13 Jun 2016 22:41:44 -0700
Message-ID: <CAAWBYDAp-w2CgLS=hR=fgDUQDLMb=YJHkjnEhV9syq2TLJfFmw@mail.gmail.com>
To: Florian Rivoal <florian@rivoal.net>
Cc: Mark Brown <mark@mercurylang.org>, "www-style@w3.org" <www-style@w3.org>
On Mon, Jun 13, 2016 at 7:34 PM, Florian Rivoal <florian@rivoal.net> wrote:
>> On Jun 14, 2016, at 04:13, Tab Atkins Jr. <jackalmage@gmail.com> wrote:
>> On Sat, Jun 11, 2016 at 12:54 AM, Mark Brown <mark@mercurylang.org> wrote:
>>> On Sat, Jun 11, 2016 at 5:42 PM, Daniel Glazman
>>> <daniel.glazman@disruptive-innovations.com> wrote:
>>>> On 11/06/2016 09:34, Sebastian Zartner wrote:
>>>>
>>>>> Coming back to this option, why is nesting the @else rule that bad? Sure, in
>>>>> other languages you have it outside of the first block, but it clearly
>>>>> connects both visually and avoids the problems of a dangling @else
>>>>> block.
>>>>
>>>> Because an invalid MQ would trash the whole thing including the nested
>>>> @else, per error handling rules...
>>>
>>> Has anyone considered something like
>>>
>>> @switch {
>>>     @case C1 { ... }
>>>     @case C2 { ... }
>>>     @default { ... }      /* optional */
>>> }
>>>
>>> ?
>>
>> That's identical to the current proposal, just with an extra level of
>> nesting.  I don't believe the current proposal is error-prone enough
>> to justify adding an additional rule.  (People don't screw up their
>> if-else chains regularly in other languages.)
>
> There would be some benefit if you compare these two things
>
> @media screen {
>  /*foo*/
> }
> @when media(width < 400px) {
>  /*bar*/
> }
> @else {
>  /*tweedledee*/
> }
>
> vs
>
> @media screen {
>  /*foo*/
> }
> @switch {
>  @case media(width < 400px) {
>    /*bar*/
>  }
>  @default {
>    /*tweedledee*/
>  }
> }
>
> They do exactly the same, but the later one is more robust to naive removal (via javascript or otherwise) of the conditional enclosing "bar". In the @when case, the @else gets mistakenly attached to the @media rule, while in the switch case it doesn't.
>
> Not that I am convinced this is worth the increase in verbosity, but it does have this advantage.

Right. Theoretically, sure, it's more robust, but it's the exact same
situation every other programming language has with something like:

if(...) {
 ...
}
if(...) {
 ...
}
else {
 ...
}

If you mistakenly delete only the middle if, the program will change
meaning, sure.  But in practice this doesn't seem to be anywhere near
hazardous enough to warrant protecting people against.  People just
don't screw this up very often.

~TJ
Received on Tuesday, 14 June 2016 05:42:35 UTC

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