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Subject: Re: [PHP-DEV] Little switch improvement: get the used variable
From: rowan.collins@gmail.com (Rowan Collins)

Christian Stoller wrote (on 25/09/2014):
> From: Rowan Collins [mailto:rowan.collins@gmail.com], Sent: Thursday, September 25, 2014 12:31 PM
>> Sorry, I was talking about this bit:
>>
>>> Currently, switch always uses a "loose" comparison (==), so cannot
>>> distinguish between "case 3" and "case 3.0". Occasionally, it would be
>>> nice to switch on a strict comparison (===); but then I thought, why
>>> stop there? What if you could use switch with any comparison operator?
>>>
>>> My idea is to give the switch() statement an optional "use" clause
>>> (since that's an existing keyword) containing a single comparison operator
>> See my earlier e-mail for examples and further details. Maybe I should
>> have given it its own thread so it was more visible; the idea has been
>> brewing for a while, I just thought this thread was a convenient place
>> to mention.
> Ah, okay, sorry.
> What do you think about that:
>
> $value = 3;
> switch (true) {
>     case 3.0 === $value: break;
>     case 3 < $value: break;
>     case 3 > $value: break;
> }
>
> Christian

When mixing operators like that, it makes sense to use that style - 
although if you're not using fallthrough, there is little advantage over 
if/elseif/else:

$value = 3;
if ( 3.0 === $value ) { }
elseif ( case 3 < $value ) { }
elseif ( case 3 > $value ) { }


At the end of the day, all control structures are glorified conditional 
jumps, and most switch statements are glorified if/else blocks. To take 
one of my examples from last night, you could write:

if ( $product instanceOf ProductInterfaces\Flight ) {
     // ...
}
elseif ( $product instanceOf ProductInterfaces\Accomm ) {
     // ...
}
else {
     // ...
}

Clearly, this works, as would the same thing using switch(true) and case 
instead of if/elseif, but the "$product instanceOf" has to be copied 
into every clause, and someone reading the code cannot assume that all 
the clauses are performing the same test.

In my proposed version, the intent is expressed more clearly, and there 
is less risk of a bug being introduced by incorrect copying or refactoring:

switch ( $product ) use ( instanceOf ) {
     case ProductInterfaces\Flight:
         // ...
     break;
     case ProductInterfaces\Accomm:
         // ...
     break;
     default:
         // ...
}

That's the idea anyway.
-- 
Rowan Collins
[IMSoP]