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Date: Wed, 25 Mar 2020 17:06:33 +0100
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Subject: Re: [PHP-DEV] [RFC] switch expression
From: php@dennis.birkholz.biz (Dennis Birkholz)

Hello together,

Am 25.03.20 um 16:46 schrieb Larry Garfield:
> On Wed, Mar 25, 2020, at 10:29 AM, Ilija Tovilo wrote:
>> Thanks for your feedback, Larry!
>>
>>> One possible improvement to either version is allowing an expression on the left side.  That is, rather than doing an equality match, do a boolean match.
>>
>> This is how Rust does it:
>>
>> ```rust
>> let x = match ... {
>>     Some(y) if y < 5 => ...
>> }
>> ```
>>
>> In other words, you can add an additional guard to each case that 
>> excepts any expression. We don't really benefit a lot from that since 
>> we don't have pattern matching. I don't think this would add any 
>> significant benefit over:
>>
>> ```php
>> $x = true switch {
>>     $x  !== null && $x < 5 => ...
>> }
>> ```
> 
> Good point, I'd forgotten about that potential trick.  So as long as an expression is allowed on the left, rather than just a literal, which is then == compared against the provided value, that should be "good enough" for most use cases.
> 
> The implementation should include some tests to make sure that works properly, but I'm happy with the resulting syntax.
> 
> So then the net result is:
> 
> $var = switch($val) {
>   case expr1 => expr2;
> }
> 
> Where $val gets compared against the result of each expr1, and if true then $var is set to expr2.

on the first glance this all looks nice but you actually created
something more like an if-expression that uses switch as a keyword
because you stripped switch of some of its major features:
- you compare the given value to possible cases -> you compare
expressions to true
- you can fall through to other cases without break
- what about the default case?

What about the following if-expression-syntax:

$var = if ($x > 0) { return 1; }
       elseif ($x < 0) { return -1; }
       else { return 0; }

Maybe this is more in line of what you want to do with your switch
expression?

Greets
Dennis