Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:79463
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain gmail.com designates 209.85.212.172 as permitted sender)
User-Agent: K-9 Mail for Android
In-Reply-To: <CAGa2bXYyvGjY3Q085CjmfEoZ6FGYRsCSsZ3mALZgeZYgD1P4uw@mail.gmail.com>
References: <CAGa2bXaAqbV4OnJSnXNboaZXD7cROR+Ue8jCE33uKci7kNo-KA@mail.gmail.com> <CAGa2bXZbD=X13wPtCHhwdO36Gki9i0wFB5=S0=GkR4WTGFEajw@mail.gmail.com> <2D560BB1-318F-461F-96CD-BE25C346E14F@gmail.com> <CAGa2bXbHKDqOA2ADrfENd+-zKknoHsvLT5WaFJay9gj1bQYOig@mail.gmail.com> <548311E6.9010406@gmail.com> <CAGa2bXYyvGjY3Q085CjmfEoZ6FGYRsCSsZ3mALZgeZYgD1P4uw@mail.gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain;
 charset=UTF-8
Date: Sun, 07 Dec 2014 09:33:24 +0000
To: "internals@lists.php.net" <internals@lists.php.net>
Message-ID: <35C29452-6E4B-455F-9084-ECA7180EB234@gmail.com>
Subject: Re: [PHP-DEV] Re: Only variables can be passed by reference
From: rowan.collins@gmail.com (Rowan Collins)

On 6 December 2014 22:25:50 GMT, Yasuo Ohgaki <yohgaki@ohgaki.net> wrote:
>Hi Rowan,
>
>On Sat, Dec 6, 2014 at 11:25 PM, Rowan Collins
><rowan.collins@gmail.com>
>wrote:
>
>> On 06/12/2014 03:03, Yasuo Ohgaki wrote:
>>
>>> Hi Rowan,
>>>
>>> On Fri, Dec 5, 2014 at 6:12 PM, Rowan Collins
><rowan.collins@gmail.com
>>> <mailto:rowan.collins@gmail.com>> wrote:
>>>
>>>     The author of function f1() presumably designed it to apply some
>>>     change to $v, rather than executing only for its side effects
>and
>>>     return value. If the caller wants to ignore this design, they
>can,
>>>     but they are not using the function as it was designed. If they
>>>     pass a function return straight into it, they have no way of
>>>     capturing the change to $v which the author intended them to
>see.
>>>
>>>
>>> The value supplied to f1() is return value.
>>> In languages, there are literal, constant and variable. Return value
>is
>>> variable.
>>>
>>
>> No, a return value is a value - it is the result of some computation
>which
>> has not yet been assigned to a variable. This is perhaps more obvious
>with
>> an operator: "1 + 2" is not a variable, it is the value 3;
>internally, a
>> temporary variable is probably used to hold that value, but that
>temporary
>> variable is never accessible to the programmer. If you have function
>> add($a, $b) { return $a + $b; }, then add(1,2) is still not a
>variable in
>> any meaningful sense.
>
>
>Value is vague term. I would like to use "expression". Expression is
>anything that has value.
>Variables/constants are values that have actual storage.
>Literals are values that may not have actual storage.
>
>Joe pointed out PHP treats temporary variable differently. I suppose
>temporary variable is created
>for values not used as usual variable. e.g. Function return value.
>
>It may be the thing we need to reconsider.
>Temporary variable is an variable after all. It may be used in context
>that
>is changed then discarded.
>
>Even if we raise errors for temporary variables, it's better to raise
>_the_same_error_ where is it allowed.
>
><?php
>define('MYERROR', -1);
>function &f1() {return -1;}  // E_NOTICE rather than E_STRICT
>function &f2() {return MYERROR;} // E_NOTICE rather than E_STRICT
>
>$v = f1();
>$v = 2;
>var_dump($v);
>
>$v = f2();
>$v = 2;
>var_dump($v);
>?>
>http://3v4l.org/9LdkK#v551
>
>I understand that return by ref and returning literal/constant is
>contradictional, yet
>it seems too much care for developers. Developer may simply return
>value
>that
>indicates some error in return by ref function should be allowed w/o
>error.
>IMHO.
>
>
>
>>  It's better to keep basic rule. IMHO.
>>>
>>> $top = array_pop(f2());
>>>
>>> is better than
>>>
>>> $v = f2();
>>> $top = array_pop($v);
>>>
>>> Is there anyone who likes latter?
>>>
>>
>> array_pop() is a stack-manipulation function, so the latter is the
>correct
>> use, with $v going on to be used as the rest of the stack. If you're
>using
>> it for something other than stack manipulation, neither is correct,
>because
>> it's the wrong choice of function.
>
>
>User may use array_slice() for it, but array_pop() is intuitive what it
>does and works
>perfectly except unneeded error. Therefore,  user surprises what is the
>"Only variable
>references should be ..." means.
>
>Anyway, I wrote a blog about this spec many years ago and the entry is
>accessed
>constantly even today.  I suppose PHP7 will have more
>intuitive/flexible
>parsing for
>complex expressions(e.g. f()[2]->method(), etc, isn't it?), then this
>spec
>may confuse
>more users.
>
>We don't need unwanted side effects, therefore this change should be
>done
>carefully.
>I wouldn't argue with this. If removing "Only variable references
>should be
>..." error is
>feasible, I would like to propose this change.


You keep talking about these "errors" being a burden on the programmer, but accepting that in principle it would be better to avoid such situations, so I want to reiterate: these are Strict Standards hints - they tell the programmer "we're not going to stop you doing this, but you might want to find a better way to write it". This seems like a perfect balance to me.