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Subject: Re: [PHP-DEV] [RFC] Skipping parameters take 2
From: rowan.collins@gmail.com (Rowan Collins)

On 20/01/2015 20:09, Marc Bennewitz wrote:
>
> Am 19.01.2015 um 19:48 schrieb Adam Harvey:
>> On 17 January 2015 at 18:04, Andrea Faulds <ajf@ajf.me> wrote:
>>> For consistency with list(), we could also just put nothing:
>>>
>>>
>>>      foo($bar, , $baz);
>>>
>>> Which is like:
>>>
>>>      list($bar, , $baz) = $arr;
>>>
>>> Thoughts?
>> That was Stas's original, original proposal way back when. I argued
>> then for having "default" as a placeholder, and still would today — in
>> the case where a function with, say, ten optional parameters[0] is
>> being called and eight of them should be the default, I think it's a
>> bit rough for somebody inheriting that code to have to count commas.
>> Having a token increases readability, IMO, and costs us nothing except
>> a few keystrokes, which isn't going to break the camel's back in a
>> language that requires "function" each time you declare a function.
>>
>> Adam
>>
>> [0] Yes, that's probably poor API design. You and I both know someone
>> will do it, though. :)
>
> Pros & Cons
>
> _Simply skipping the argument out:_
> pro:
>     - same syntax as skipping entries used by `list`
> con:
>     - hard to read and to differ from mistakes
>     - not an option for inheritance
>
> _Using the keyword `default`:_
> pro:
>     - better to read and to differ from mistakes
>     - usable on inheritance
> con:
>     - different syntax as `list`
>     - not possible as alternative syntax for `list` as it has no 
> "default" naming
>
> _Using a special character:_
> pro:
>     - better to read and to differ from mistakes
>     - usable on inheritance
>     - possibly an alternative syntax for `list` (for consistency)
> con:
>     - different syntax as `list`
>     - Not a good character found for it, yet
>
> _Named Parameters:_
> pro:
>     - readability  (If caller is not required to call as assoc array)
>     - not an option for inheritance
> con:
>     - paramter skipping is a side product with possible edge cases
>     - Adds variable names to be part of the API
>     - implementation complexity
>
> In my opinion plain skipping parameters is a nice addition to PHP even 
> if named arguments will be introduced.
>
> A special character would indeed the best option but as long as there 
> is no good character it's not an option.

Nice summary. My only difference of opinion would be that a special 
character, even if a good candidate were found, should be listed as 
"pros: better readability than simply skipping; cons: worse readability 
than a keyword". Punctuation is never going to be as intuitive as a 
well-chosen keyword for someone new to the feature.

It certainly has advantages in applicability to multiple situations, 
though. The mention of for..in elsewhere made me wonder about a syntax 
for discarding the values of an array when looping over its keys; if _ 
were available as a default/skip token, you could write:

foreach ( $foo as $key => _ ) { ... }

That doesn't make sense with the "default" keyword, although a different 
keyword might fit multiple use cases, e.g. "skip":

func_with_many_args(42, skip, skip, false);
list($foo, skip, $bar) = $some_array;
foreach ( $foo as $key => skip ) { ... }

That actually reads quite well to me, but obviously requires reserving a 
new keyword, and breaking compatibility if any code has a constant named 
"skip".

Regards,

-- 
Rowan Collins
[IMSoP]