Re: Generators in PHP

On 08/08/12 21:14, Nikita Popov wrote:

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. “Sending values” section seems to be missing. Especially useful would be to cover what happens with keys there and what is the syntax there - is it just "$a = 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 = yield;
     $data = (yield $value);
     $data = (yield $key => $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 Hi Nikita,

I notice you require brackets round yield $k => $v and yield $v. Is this the formal syntax, i.e. '(' T_YIELD var => var ')'? If so it makes sense in a way, but it feels a little hackish. Does yield $v cause some sort of parsing issue that putting it in brackets solves? I realise that it's less ambiguous, but I don't like the idea of it. PHP's syntax has enough special cases already IMO. Regards, -- Andrew Faulds http://ajf.me/