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Date: Tue, 26 Feb 2013 20:08:47 +0300
Message-ID: <CA+9eiLu9f_gANN4az4gqG7L3Obf0dE2110fBUooOYt6bvxJy0A@mail.gmail.com>
To: Nikita Popov <nikita.ppv@gmail.com>
Cc: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Allow (...)->foo() expressions not only for `new`
From: dmitry@zend.com (Dmitry Stogov)

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On Tue, Feb 26, 2013 at 8:49 PM, Nikita Popov <nikita.ppv@gmail.com> wrote:

> On Tue, Feb 26, 2013 at 7:41 AM, Dmitry Stogov <dmitry@zend.com> wrote:
>
>> Hi Nikita,
>>
>> I like the idea.
>> But note, that it may cause some unexpected behaviour and bugs.
>> I didn't test the patch I just guess it on my previous experience
>> introducing similar features.
>>
>> - usage expression in write context (e.g. passing constant by reference)
>>
>> function foo(&$foo) {}
>> foo("abc"[0]);
>>
>> - destruction of temporary result
>>
>> ($a . $b)[4]; // if ($a.$b) is destroyed?
>>
>> - in some cases destruction of temporary result may cause destruction of
>> final result
>>
>> ((object)(array("a"=>"b")))->a = "c"; // temporary object may be
>> destroyed before assignment
>>
>> All these edge cases must be carefully analyzed.
>> I like the current patch, and in case the edge cases won't require many
>> hacks, I'm all for it.
>>
>> Thanks. Dmitry.
>>
>
> I just played a bit with it and came up with the following (additional)
> patch to support use in write context:
> https://github.com/nikic/php-src/commit/31705dd8c53efe3bb52d6aae483a324e5a511ae9It throws an error if the write is done on a TMP or CONST,
>

I like this patch more (it doesn't complicate executor).
However it doesn't handle BP_VAR_FUNC_ARG, where decision about read/write
context must be done at run-time.


> but things like (new foo)->bar = 'x' will work. Though I'm not quite sure
> whether this is really necessary, at least I don't see much use for it.
>
>

no sense, but it may call __set() magic method, that may print something,
clobber something, throw exception, etc...


> Reading your mail again, I missed the second point (about destruction of
> temporary). But I wonder how it could cause any issue. I mean, FREE op is
> only inserted when expression is used as statement, which is not the case
> here. Or am I missing something?
>
>
Actually, I think IS_TMP operands shouldn't make any problems, but I can't
be completely sure.

Thanks. Dmitry.

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