Re: [RFC] Skipping parameters take 2

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]