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Subject: Re: [PHP-DEV] [RFC Discussion] Typed Properties
From: dmitry@zend.com (Dmitry Stogov)

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On 03/30/2016 06:16 AM, Joe Watkins wrote:
> Morning Dmitry,
>
> > 1) static typed properties are prohibited. why?
>
> Feels like that's a separate feature, static properties are as good as 
> makes no difference, global variables.

 From the user perspective there is not a lot of difference between 
regular and static properties.

> Instance properties, the engine has good control over their 
> manipulation, for static properties it doesn't, it's not impossible, 
> but feels separate.

so this is an implementation problem.

>
> > 2) The handling of multiple properties in the same declaration 
> statement is inconsistent.
>
> This feels consistent to me .. in other languages where the type is 
> required, it makes sense to assume the type is implied.
>
> In a language where the type is optional, public int $foo, $bar; feels 
> ambiguous to me.

But this is the valid syntax for others. And this is going to be yet 
another reason to blame PHP.

>
> > 3) We already have nullable arguments without any special syntax. We 
> should reuse the similar approach for properties.
>
> Making properties implicitly nullable defeats the object of trying to 
> provide type safety.
>
> Null is never a valid value for a typed property, if it were, you 
> would never be sure of the type of variable you are getting, and would 
> have to litter your code with is_null checks.

If we use one rule for arguments, why should we invent others. 
Properties are going to be nullable only if you explicitly initialise 
them with NULL.

>
> > I think it might be better to implicitly initialize them according 
> to type (if default value is not provided): bool by false, int by 0, 
> double by 0.0, string by "" (interned), array by [] (immutable), 
> objects by NULL (always nullable).
>
> Definitely not, lying about the default value isn't a good idea.
>
> There are times when 0 is as valid as 1, or any other value for an int.
>
> If you have declared that you know the type of the property, and you 
> write code that accesses that property before there is any possible 
> chance you have set the property, that's a programming error.
>
> We should not hide that error with a default value, or by allowing the 
> engine to return null.

Your arguments may make sense, but PHP never required property 
initialization. Introducing orthogonal rules for typed properties seems 
strange.

>
> > We can't change property_info->type_ce for internal properties, 
> because they are shared between threads.
>
> I'm not sure what to do about that ... will think ...
may be it's possible to make a special pass at the end of MINIT to 
initialize all property_info->type_ce, for all internal classes.

> 6) and 7) and 8) just sound like bugs ... will look at those ...
>
> 9) I always intended to leave that to you :)

I'll spend some time trying to find a good solution.

Thanks. Dmitry.

>
> Cheers
> Joe
>
>
> On Tue, Mar 29, 2016 at 11:59 PM, Dmitry Stogov <dmitry@zend.com 
> <mailto:dmitry@zend.com>> wrote:
>
>     Hi,
>
>     Reviewing the patch sources I found few inconsistent decisions not
>     mentioned in RFC.
>
>     1) static typed properties are prohibited. why?
>
>     2) The handling of multiple properties in the same declaration
>     statement is inconsistent.
>
>             public int $bar, string $qux; // this works
>
>             public int $bar, $qux; //this emits error: Untyped
>     property A::$qux must not be mixed with typed properties
>
>     It's better to allow type only before first property in the list
>     and apply them to all of them (like C, Java and others).
>     Is this just an implementation issue?
>
>     3) We already have nullable arguments without any special syntax.
>     We should reuse the similar approach for properties.
>
>     public int $num = null;
>
>     4) There's a mess with initialization of typed properties. (typed
>     properties are initialized by IS_UNDEF, untyped by IS_NULL).
>     I think it might be better to implicitly initialize them according
>     to type (if default value is not provided): bool by false, int by
>     0, double by 0.0, string by "" (interned), array by []
>     (immutable), objects by NULL (always nullable).
>
>     Also I found a number of implementation problems:
>
>     5) We can't change property_info->type_ce for internal properties,
>     because they are shared between threads.
>     Can property of Internal class have a type of user class? This
>     would lead to crash on second request.
>
>     6) $x->a++; doesn't throw on overflow
>
>     7) ++$a->a; and += throw on overflow, but change the property
>     value to "float"
>
>     8) Reference handling in ZEND_FETCH_OBJ_W is not robust. At least,
>     EXT_NOP or TICK may be inserted before next ASSIGN_REF. Handling
>     of ZEND_ADD_ARRAY_ELEMENT and ZEND_YIELD is too pessimistic,
>     missing support for SEND_REF and may be others.
>
>     9) Often calls to zend_object_fetch_property_type_info() are not
>     good for performance. Currently FETCH_OBJ_X cache "offset" to
>     property, in general we may go back and cache address of
>     "property_info", but this is going to decrease performance for
>     each property access. It would be great to find a better solution.
>     May be using zval.reserved.
>
>     I assume, I didn't find all problems yet.
>
>     I think, both RFC and implementation have problems.
>     I may try to help with implementation.
>     (9) is the most difficult problem, and I'll try to solve it first.
>     Do you see any problems with updating RFC with (2), (3), (4)?
>     (1) would also make proposal more consistent, but I assume you got
>     some troubles implementing it and I don't know about them yet.
>
>     Thanks. Dmitry.
>
>
>     ________________________________________
>     From: Dmitry Stogov <dmitry@zend.com <mailto:dmitry@zend.com>>
>     Sent: Tuesday, March 29, 2016 19:24
>     To: Joe Watkins
>     Cc: Phil Sturgeon; krakjoe@php.net <mailto:krakjoe@php.net>;
>     internals@lists.php.net <mailto:internals@lists.php.net>
>     Subject: Re: [PHP-DEV] [RFC Discussion] Typed Properties
>
>     Thanks. I'll start tomorrow morning and will try to send you
>     update by the evening,
>
>     ________________________________
>     From: Joe Watkins <pthreads@pthreads.org
>     <mailto:pthreads@pthreads.org>>
>     Sent: Tuesday, March 29, 2016 19:18
>     To: Dmitry Stogov
>     Cc: Phil Sturgeon; krakjoe@php.net <mailto:krakjoe@php.net>;
>     internals@lists.php.net <mailto:internals@lists.php.net>
>     Subject: Re: [PHP-DEV] [RFC Discussion] Typed Properties
>
>     Hi Dmitry,
>
>         The patch is pretty close to complete.
>
>         When you start to dig a bit further, you'll notice that I
>     prepared for using cached pointers to prop info, but, I'm not sure
>     how to allocate those as the handlers are using the currently
>     allocated slots so differently.
>
>         I also patched opcache, but it's probably wrong (or not good
>     enough, not sure what to do about type_ce).
>
>         Please do start working on the patch, that would be great ...
>     I'll leave it alone for you to do your thing :)
>
>     Cheers
>     Joe
>
>     On Tue, Mar 29, 2016 at 5:12 PM, Dmitry Stogov <dmitry@zend.com
>     <mailto:dmitry@zend.com><mailto:dmitry@zend.com
>     <mailto:dmitry@zend.com>>> wrote:
>     Hi Phil, hi Joe,
>
>     Is your patch complete?
>
>     I took just a brief review yet, and I would like to make a deep
>     check once again (and may be optimization).
>     I saw, the patch makes some slowdown, but less than I expected.
>     If you are not going to modify the patch in next two days, I would
>     start working on it tomorrow.
>
>     RFC itself looks fine.
>
>     Thanks. Dmitry.
>
>     ________________________________________
>     From: Phil Sturgeon <pjsturgeon@gmail.com
>     <mailto:pjsturgeon@gmail.com><mailto:pjsturgeon@gmail.com
>     <mailto:pjsturgeon@gmail.com>>>
>     Sent: Tuesday, March 29, 2016 18:32
>     To: Andrey Andreev
>     Cc: internals@lists.php.net
>     <mailto:internals@lists.php.net><mailto:internals@lists.php.net
>     <mailto:internals@lists.php.net>>
>     Subject: Re: [PHP-DEV] [RFC Discussion] Typed Properties
>
>     I'd like to thank everyone for their feedback on this RFC!
>
>     It looks like the majority of concerns were solved during the course
>     of this discussion, which is great news.
>
>     The RFC has been expanded in a few areas to take care of a few other
>     concerns, so please go and review it and let me know if you have any
>     feedback.
>
>     https://wiki.php.net/rfc/typed-properties
>
>     Voting will start in a few days.
>
>     Cheers,
>     Phil
>
>     --
>     PHP Internals - PHP Runtime Development Mailing List
>     To unsubscribe, visit: http://www.php.net/unsub.php
>
>


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