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Date: Sun, 25 Aug 2024 11:01:38 +0100
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Subject: Re: [PHP-DEV] [RFC] Default expression
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From: bilge@scriptfusion.com (Bilge)

On 25/08/2024 10:49, Juliette Reinders Folmer wrote:
> (resending as I accidentally originally send a private reply instead 
> of sending the below to the list)
>
> On 24-8-2024 18:49, Bilge wrote:
>> Hi gang,
>>
>> New RFC just dropped: https://wiki.php.net/rfc/default_expression. I 
>> think some of you might enjoy this one. Hit me with any feedback.
>>
>> This one already comes complete with working implementation that I've 
>> been cooking for a little while. Considering I don't know C or PHP 
>> internals, one might think implementing this feature would be 
>> prohibitively difficult, but considering the amount of help and 
>> guidance I received from Ilija, Bob and others, it would be truer to 
>> say it would have been more difficult to fail! Huge thanks to them.
>>
>> Cheers,
>> Bilge
>>
>
> Hi Bilge,
Hi :)
> I like the idea, but see some potential for issues with ambiguity, 
> which I don't see mentioned in the RFC as "solved".
>
> Example 1:
> ```php
> function foo($paramA, $default = false) {}
> foo( default: default ); // <= Will this be handled correctly ?
> ```

No, but not because of my RFC, but because $paramA is a required 
parameter that was not specified. Assuming that was just a typo, the 
following works as expected:

function foo($paramA = 1, $default = false) {
     var_dump($default);
}
foo(default: default); // bool(false)

> Example 2:
> ```php
> callme(
>     match($a) {
>         10 => $a * 10,
>         20 => $a * 20,
>         default => $a * default, // <= Based on a test in the PR this 
> should work. Could you confirm ?
>     }
> );
> ```
Yes.
> Example 3:
> ```php
> switch($a) {
>     case 'foo':
>         return callMe($a, default); // I presume this shouldn't be a 
> problem, but might still be good to have a test for this ?
>     default:
>         return callMe(10, default); // I presume this shouldn't be a 
> problem, but might still be good to have a test for this ?
> }
> ```
Yes.
> On that note, might it be an idea to introduce a separate token for 
> the `default` keyword when used as a default expression in a function 
> call to reduce ambiguity ?
Considering the Bison grammar compiles, I believe there can be no 
ambiguity. I specifically picked `default` because I think it is the 
most intuitive keyword to use for this, and it's conveniently already a 
reserved word.

Cheers,
Bilge