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Date: Tue, 22 Jan 2013 17:20:28 +0100
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Subject: Re: [PHP-DEV] [VOTE] Property Accessors for 5.5
From: gooh@php.net (Gordon Oheim)

Am 22.01.2013 02:46, schrieb Clint Priest:
>
> On 1/20/2013 3:11 PM, Gordon Oheim wrote:
>> Am 17.01.2013 19:20, schrieb Clint Priest:
>>> I'm happy to say that Property Accessors is ready for a vote for
>>> inclusion in 5.5 release.
>>>
>>> Nikita and I (as well as Stas a bit) have all been working hard to make
>>> this happen for 5.5, voting and the specifications are here:
>>>
>>> https://wiki.php.net/rfc/propertygetsetsyntax-v1.2#voting
>>>
>>> Thanks,
>>>
>>> -Clint
>>
>> Thanks Clint and Niki for your work. Sorry to respond only now that
>> the voting process has already started. I usually don't
>> follow/participate on internals due to the noise and poisoned
>> atmosphere (but that's a different story). Also thanks Niki for taking
>> the time to answer all my questions I had about this beforehand.
>>
>> My main issue with the implementation at hand is the weird way in
>> which we allow the visibility on the properties to be declared, e.g.
>>
>>     public $foo { get; protected set; }
>>
>> The visibility keyword on the property is watering down the visibility
>> semantics. Either the property is public (then it can be set) or it is
>> not public. I would have much less of a problem with this, if
>> declaring visibility on a property could only be loosened but not
>> tightened. That would at least be consistent with how visibility works
>> with inheritance. It would be much better though to remove the
>> visibility keyword from the property altogether. It almost never tells
>> the truth.
>
> This is basically an argument against asymmetrical visibility altogether
> which is one of the most useful features of this proposal.  I think
> there are many use cases where an object wants to be able to emit a
> message (value) but not receive one and being able to declare that fact
> is important.
>

I understand the purpose and utility of having different levels of 
visibility. I am not argueing against that. I am argueing that putting 
the visibility on the property does not give accurate information about 
the property's visibility itself.

Contrived Example: doing just public $foo (Traditional Property) means I 
can access the property from everywhere directly. But doing public $foo 
{} (Guarded Property) means I cannot access the property *at all*. So we 
went through full access to no access just by adding curly braces. 
Likewise, private $foo { public get; public set; } is not private at all.

When the visiblity only applies to declared accessors we should just 
declare in on the accessors only. That makes for better semantics. After 
all, it's a guarded property, which already implies that it is hidden 
behind accessors and thus non-public.

>> Removing the visibility keyword from the property altogether would
>> also remove the purported default visibility that is applied to the
>> accessors. I say "purported" because doing
>>
>>     public $foo { get; protected set; }
>>
>> will also change the unset accessor to protected, which makes perfect
>> sense when you think about it but is completely unobvious when the
>> declaration claims the default visibility of all accessors to be
>> public. The default visibility of isset is that of get and the default
>> visibility of unset is that of set instead.
>>
>> To add to the confusion, doing
>>
>>     public $foo { get; protected set; public unset; }
>>
>> WILL work and change the visibility of unset back to what the property
>> claims it is. This should not be necessary when visibility on the
>> keyword defines the default visibility. I guess it's safe to say that
>> having the visibility on the property does very little to express
>> anything meaningful about the property or the default visibility of
>> *all* the accessors.
>>
> Perhaps this is just a documentation problem in that somewhere the
> implication that public applies to all accessors when it should really
> say that it applies to all declared accessors.

Yes, that should be stretched. I think the final documentation should 
also strongly emphasize that Guarded Properties is an entirely new 
concept and not some extension to Traditional Properties or to Magic 
Methods. We should prevent people from trying to map these new Guarded 
Properties onto their existing mental models of how Traditional 
Properties or Magic Methods work.

>
> It is perfectly logical that when you cannot set a value, then you
> cannot unset a value.
>
> Defining what you have done above is declaring that you want to allow
> people to get or unset the value, but not set it directly. This makes
> sense in some usage scenarios.  As an example, perhaps $foo represents
> an internally generated id which is generated on the first call to the
> getter, you don't want outsiders to specify the id, but you're okay with
> having it unset so that a new one can be generated with the internal
> generation mechanics on the next get request.
 >
> As an aside, your previous example can also be declared like this:
>      public $foo { get; protected set; unset; }
>
> unset is explicitly declared and implicitly implemented and is public,
> isset would be implicitly declared and implicitly implemented and follow
> the visibility of the getter.
>
> isset/unset only follow the get/set visibility if isset/unset are left
> undeclared.

I agree that set and unset would usually have the same visibility, but I 
do not agree that this should happen magically. Implicit means hidden 
and hidden always leads to WTF moments. I understand the convenience of 
having this happen automatically when this is how you'd use it most of 
the time. But it's still a side-effect and your UseCase shows there are 
exceptions where you would not want to have it that way. Maybe it should 
just not happen silently?

>>
>> If this could be changed, I'd be more willing to vote pro the proposal.
>>
>> TL;DR: The visibility keyword on the property is almost never giving
>> an accurate information about the accessor visibility. Thus, it should
>> be removed or replaced for clarity's sake.
>
> I think I've made the case above that this isn't accurate, it always
> affects declared accessors which do not have their own visibility
> specified.
>

Thanks for your clarification. I'd still favor dropping the visibility 
from the property though. Your summary of what the visibility does is 
giving a clear description of the problem I see: the visibility is not 
about the property at all (like it is with traditional properties) and 
it only affects a subset of accessors (declared ones).

>>
>> Regards,
>> Gordon
>>
>