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Date: Mon, 23 Sep 2013 23:18:39 +0200
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Subject: RE: [PHP-DEV] Argument unpacking - Multiple unpacks and trailing arguments
From: rstoll@tutteli.ch ("Robert Stoll")



> -----Original Message-----
> From: Lars Strojny [mailto:lars@strojny.net]
> Sent: Monday, September 23, 2013 9:37 PM
> To: Nikita Popov
> Cc: PHP internals
> Subject: Re: [PHP-DEV] Argument unpacking - Multiple unpacks and trailing
> arguments
> 
> Hi Nikita,
> 
> Am 23.09.2013 um 21:33 schrieb Nikita Popov <nikita.ppv@gmail.com>:
> [...]
> > An example of trailing arguments are array intersections and diffs
> > using a custom compare function:
> >
> >    array_uintersect(...$arrays, $compare);
> >    array_udiff(...$arrays, $compare);
> >    // also array_intersect_uassoc and all those other variations on
> > the topic
> >
> > Some people expressed concern about allow both usages (multiple
> > unpacks / trailing args). I have a bit of a hard time understanding
> > this (as there clearly are practical applications for both), so I'd
> > appreciate some more opinions on the topic.
> 
> Although it might allow users to shoot into their foot, I prefer having it
> instead of introducing a limitation that is not technically necessary. So
+1
> 
> cu,
> Lars
[Robert Stoll] 
Personally I would allow multiple unpacking but not allow unpacking for
non-variadic parameters thus:

function foo(...$arr){}  foo(...$arr, ...$arr2); //is fine
function foo(...$arr){}  foo(1, 2, ...$arr, ...$arr2); //is fine
function foo($foo, $bar, ...$arr){} foo(1,2,...$arr, ...$arr2); //is fine as
well
function foo($foo, $bar, ...$arr){} foo(1, ...$arr, ...$arr2, 2);
//shouldn't be allowed IMO - ...$arr is not passed to a variadic parameter

And I would definitely not allow things like the following (but I think you
removed it already from the RFC)

function foo($bar, $baz, $buz, $boz, $booz, $booze){} 
foo(..$arr, 2, ..$arr2);

I think the readability is harmed when the user is not able to tell directly
which arguments are passed to which parameters. For instance:
function foo($foo, $bar){}
function bar($foo, $bar, ...$arg){}

function doIt(Iterator $iterator){ 
    foo(...$iterator);
    bar(...$iterator);
}

Depending on the implementation of $iterator the value passed to the
parameters $foo and $bar will be different (regardless of the ...$arg in
function bar) and you will have a hard time to understand the code quickly.
As far as I understood PHP should be easy learnable, I think doing unpacking
arguments in a wrong way can hinder this and the language should restrict
it.

IMO the implementation of array_uintersect should follow the same rule as
variadics in a later version (6.x or whatever)

Cheers,
robert