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Date: Sat, 18 Aug 2012 15:29:23 +0200
Message-ID: <CAF+90c_wks01FMOFCLxenN_Rb95x+SDL2y7YYvx=BdH9Cuc=eg@mail.gmail.com>
To: Sherif Ramadan <theanomaly.is@gmail.com>
Cc: Larry Garfield <larry@garfieldtech.com>, internals@lists.php.net
Content-Type: text/plain; charset=ISO-8859-1
Subject: Re: [PHP-DEV] Re: Generators in PHP
From: nikita.ppv@gmail.com (Nikita Popov)

On Thu, Aug 9, 2012 at 4:49 AM, Sherif Ramadan <theanomaly.is@gmail.com> wrote:
>>
>> One question, though: It looks based on the voting like finally {} blocks
>> are going in.  So... what should happen in the following situation:
>>
>> function stuff() {
>>   try {
>>     foreach (range(1, 100) as $i) {
>>       yield $i;
>>     }
>>   }
>>   finally {
>>     print "All done";
>>   }
>> }
>>
>> Does "All done" get printed once, or 101 times?  Similarly:
>>
>> function things() {
>>   $i = 1;
>>   try {
>>     while (true) {
>>       yield $i++;
>>     }
>>   }
>>   finally {
>>     print "All done";
>>   }
>> }
>>
>> That will run indefinitely.  So will "All done" ever print, or does that
>> finally become unreachable?
>>
>> (I have no clue what the behavior "should" be in these cases, just that it
>> should be sorted out sooner rather than later.)
>>
>
>
> Based on my understanding of both RFCs, I don't see that this would be
> a conflict or lead to unexpected behavior. As stated by the generators
> RFC: "When you first call the generator function ($lines =
> getLinesFromFile($fileName)) the passed argument is bound, but nothing
> of the code is actually executed. Instead the function directly
> returns a Generator object.".
>
> So in the event we are calling the function stuff(), nothing should
> actually be executed, and as we iterate over the traversable object
> the generator should be "passing control back and forth between the
> generator and the calling code". This would be indicated by the
> "yield" keyword present in the function. Meaning you should see the
> expected result and finally should only ever be called once in your
> first example.
>
> As for you second example... Obviously if you've created an infinite
> loop you've made everything outside of the loop unreachable, whether
> you're using generators or not.
>
> However, I'll let the author of the RFC provide any clarification or
> corrections where I might be wrong.

Yes, that is basically right. The one interesting case that arises
when using generators is what happens when you close a generator
before it is finished. E.g. in the function mentioned above:

function stuff() {
    try {
        foreach (range(1, 100) as $i) {
            yield $i;
        }
    } finally {
        print "All done";
    }
}