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Date: Fri, 13 May 2016 11:16:17 -0700
Message-ID: <CAESVnVrn6iSZ7KWVDpcJ-Fw7k9NZnUbHUs88RBOBPsENg_sVWQ@mail.gmail.com>
To: =?UTF-8?Q?Fran=C3=A7ois_Laupretre?= <francois@php.net>
Cc: Zeev Suraski <zeev@zend.com>, Quim Calpe <quim@kalpe.com>, "davey@php.net" <davey@php.net>, 
	Larry Garfield <larry@garfieldtech.com>, 
	"internals@lists.php.net" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] Pipe Operator
From: pollita@php.net (Sara Golemon)

On Fri, May 13, 2016 at 10:18 AM, Fran=C3=A7ois Laupretre <francois@php.net=
> wrote:
>> So we'd have to audit all 4k+ functions in the PHP runtime (and
>> provide a mechanism for defining it on userspace functions)?
>
> That's right, except that, if we only consider functions accepting more t=
han
> 1 arg, we just need to check about 1,000 functions. It may seem a lot but=
,
>
Having been a large part of the audit for PHP6, I'd say "Yes, it
definitely seems like a lot, and is." :p

> for a potential solution to such a long-time issue as argument ordering
> sadness, IMHO, it's worth the pain. I am currently doing it and I'll send
> you the list when it is ready.
>
Awesome.  Even if not used in this feature, it could potentially be
useful elsewhere.  I hope you put it in a public gist or similar for
posterity.

> For userspace functions, the logic can be quite simple : 0 arg -> not usa=
ble
> in a pipeline, 1 arg or more -> substitute first arg. Then, we have 4
> options :
>         - consider that, when using a userland function in a pipeline, th=
e
> lhs is always inserted in 1st position,
>
It would feel weird that internal functions can deviate from this
rule, but user-space functions can't. :/

>         - provide a function to change the position on an existing functi=
on
> (default =3D 0 when function is registered). A negative position would di=
sable
> using the function in a pipeline,
>
Feels like a hack, but I suppose if it were part of Reflection it
might make sense...

(new ReflctionFunction('my_func')->setPipeArgPosition(3);

>         - enrich the syntax of function declaration to designate the arg =
to
> substitute.
>
This would be a good application for User Attributes:

<<__PipeArg(1)>>  // Zero based, obv
function array_map(Callable $fn, array $arr) {...}


> I would propose to start with the 1st choice. After people have the occas=
ion
> to use it for a while, we will see if an additional mechanism is requeste=
d.
>
That's not unreasonable if we're starting from a place of assuming
that invisible substitution is the way to go.  I'm not convinced, but
I could be.

Just to verify, you're suggesting an end-state something like this?

$ret =3D array(1,2,3)
  |> array_map(function($x) { return $x * 2; }) // lhs implicitly
passed as second arg
  |> array_sum(); // implicitly passed as only arg (first position)
// $ret =3D=3D=3D int(12)

-Sara