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Date: Tue, 19 Sep 2017 16:46:16 -0600
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To: Sara Golemon <pollita@php.net>
Cc: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] Pre-draft for PipeOp v2
From: levim@php.net (Levi Morrison)

On Tue, Sep 19, 2017 at 4:32 PM, Sara Golemon <pollita@php.net> wrote:
> I was planning to update the RFC, but wiki.php.net is having issues
> atm and isn't coming back up with basic coaxing, so I'll just start
> discussion informally, and the RFC can be updates later.
>
> Background: I made an RFC some time ago to implement HackLang's Pipe
> Operator https://docs.hhvm.com/hack/operators/pipe-operator which
> provides fluent calling for non-object interfaces.
> I circulated it to mixed reviews, many negative, with the negativity
> feeling like it centered on the use of a magic placeholder token `$$`.
>
> After discussion with Levi and others who suggested a simpler
> approach, I'd like to offer
> https://github.com/php/php-src/compare/master...sgolemon:pipe2 as an
> alternate possibility.
>
> This version removes the $$ token, and instead treats the RHS of the
> expression as a callable obeying the same rules as the callable
> typehint elsewhere in the language.  Specifically:
> * Free functions as strings containing the function name. (e.g. 'funcname')
> * Object methods as array($object, 'methodname')
> * Static methods as array('Classname', 'methodname')
> * Closure expression (e.g.  function($x) { return ...; }  )
> * Object instance with an __invoke() method.
>
> In a given pipe expression, the output of the LHS expression feeds a
> single arg to the callable on the RHS.
> Examples:
>
> $x = "hello"
> |> 'strtoupper'
> |> function($x) { return $x . " world"; };
> // $x === "HELLO world"
>
> Non-Goal: I didn't include support for base function names (e.g.
> `"hello" |> strtoupper`) because of the conflict with constants.
> Using a constant to store your function name is totes legit and
> consistent with language syntax.
>
> Future Scope: Short Lambdas `$x => $x + 1` and Partial Functions
> `someFunc('fixed val1', ..., 'fixed val2')`  would help make this
> functionality more useful and are worth discussing as a sub-thread,
> but are not required to be implemented at the same time.
>
> -Sara
>
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Thank you for making this proposal! As alluded to I had concerns on
the original proposal and fully support this version. Sometimes
simplicity is the mark of a good RFC and I think this is one of those
times.