Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:62086
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain gmail.com designates 209.85.215.42 as permitted sender)
MIME-Version: 1.0
In-Reply-To: <CAF+90c-w_1H8Raq90AzM3B7Fw67Ss-dCOi-8p_KxkGVj8-T9rA@mail.gmail.com>
References: <CAF+90c_47HtYHnMztUUb7Gd5_gKhpJYJN=G-KJFSmSt_=w2+Lw@mail.gmail.com>
	<50108D60.9090509@sugarcrm.com>
	<CAF+90c-w_1H8Raq90AzM3B7Fw67Ss-dCOi-8p_KxkGVj8-T9rA@mail.gmail.com>
Date: Wed, 8 Aug 2012 22:14:56 +0200
Message-ID: <CAF+90c936qah8bsBzdZh3Q_oPe2wvyp0AzZUwDa_Y+PoJ0wayg@mail.gmail.com>
To: Stas Malyshev <smalyshev@sugarcrm.com>
Cc: Nikita Popov <nikita.ppv@googlemail.com>, PHP internals <internals@lists.php.net>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: quoted-printable
Subject: Re: [PHP-DEV] Generators in PHP
From: nikita.ppv@gmail.com (Nikita Popov)

On Fri, Jul 27, 2012 at 8:09 PM, Nikita Popov <nikita.ppv@gmail.com> wrote:
>> 5. Are multiple yields allowed? I.e. the rfc mentions something like
>> yield yield $a - what that would mean? I'd allow yield only be applied
>> to variable expression (lval) because double yield doesn't make sense to
>> me, but maybe I miss something.
>
> yield yield $a would basically first yield $a and then receive some
> value (via send) and yield that value again. Nothing you'd normally do
> ;) It was mentioned only as a syntax ambiguity consideration.
>
> Actually I added some additional parenthesis requirements for yield.
> For example you'd have to write the above as `yield (yield $a)` now
> (which should be slightly more clear). I haven't yet reflected this
> change in the RFC, but I'll add a section on it later.
>
>> 6. =93Sending values=94 section seems to be missing. Especially useful w=
ould
>> be to cover what happens with keys there and what is the syntax there -
>> is it just "$a =3D yield;"? Or does it mean when yield is used in
>> expression it becomes incoming yield? And, last but not least - do we
>> need sending into generators at all?
>
> Yeah, I haven't written that section yet. But it is fairly simple: If
> you go $generator->send($foo) then $foo will be the result of the
> current `yield` expression. And yes, this also works with keys and
> values. All of the following are valid:
>
>     $data =3D yield;
>     $data =3D (yield $value);
>     $data =3D (yield $key =3D> $value);
>
> The first case is the most common though. I.e. you usually use it
> either as a generator or a reverse generator, not both. But doing both
> is also common for cooperative multitasking etc.
>
> Regarding the last question: I think the feature is worth adding. It
> is a very powerful concept that is hard to implement otherwise. Useful
> in particular for things like parsing and multitasking.
>
>> 6. What happens if you send into a by-ref generator? Is the data sent
>> by-ref then? What if it's an expression that can't be send by-ref?
>
> No, sending is always by-value. By-ref only affects the yielding part.

I now added the mentioned sections:

https://wiki.php.net/rfc/generators#yield_keyword
https://wiki.php.net/rfc/generators#sending_values

I also added a list of error conditions:

https://wiki.php.net/rfc/generators#error_conditions

Sorry for the delay,
Nikita