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April 03, 2012
Re: traits getProtection
Le 02/04/2012 22:59, Simen Kjærås a écrit :
> On Mon, 02 Apr 2012 20:02:20 +0200, deadalnix <deadalnix@gmail.com> wrote:
>
>>> Now, there are a number of people very unhappy about this state of
>>> affairs and
>>> want private to hide symbols as well (personally, I think that the
>>> fact that
>>> it makes private aliases effectively useless is reason enough to
>>> seriously
>>> reconsider the current behavior), but I don't know if there's any
>>> real chance
>>> of convincing Walter or not.
>>>
>>
>> This would be a huge mistake. For instance, private method are
>> sometime meant to be overridden in subclasses, which is impossible if
>> symbol is inaccessible.
>>
>> NVI for instance would be impossible in such a situation.
>
> NVI is perfectly possible with protected.

You'll loose the ability to define a function, without being able to 
call it.

It is something you want if function have to be called by pair for 
example (using protected here would introduce temporal coupling). It 
make even more sense if you consider combining it with contract programing.
April 03, 2012
Re: traits getProtection
Le 03/04/2012 00:00, Timon Gehr a écrit :
>
> Making private symbols invisible to other modules or at least excluding
> them from symbol clashes is necessary. The current behaviour is not
> useful or desirable in any way.
>

This smells like religious coding to me.

>> NVI is perfectly possible with protected.
>
> Exactly. Furthermore, private implies final anyway.

Which is complete bullshit. Even in a module you may want to override a 
method.
April 03, 2012
Re: traits getProtection
On 04/03/2012 08:27 AM, deadalnix wrote:
> Le 03/04/2012 00:00, Timon Gehr a écrit :
>>
>> Making private symbols invisible to other modules or at least excluding
>> them from symbol clashes is necessary. The current behaviour is not
>> useful or desirable in any way.
>>
>
> This smells like religious coding to me.
>

Nope.

>>> NVI is perfectly possible with protected.
>>
>> Exactly. Furthermore, private implies final anyway.
>
> Which is complete bullshit.

It is a questionable design decision. It might be reasonable to allow 
overriding private members, but that would mess with the vtable layout.

> Even in a module you may want to override a
> method.

... which is excluded from the public interface. There are better ways 
to hide a method than to mark it private in an implementation class.
April 03, 2012
Re: traits getProtection
On Mon, 02 Apr 2012 08:05:09 -0500, Dmitry Olshansky <dmitry.olsh@gmail.com> wrote:

> On 02.04.2012 16:04, Adam D. Ruppe wrote:
>> On Monday, 2 April 2012 at 09:26:07 UTC, Dmitry Olshansky wrote:
>>> It's all nice and well, but I believe part of the reason of say
>>> private protection is that user is never ever able to see(!) it. Thus
>>> it user can't depend on private members being there, which is a good
>>> thing.
>>
>> That's not the way it is right now in D: if you use the
>> reflection traits, you can see and access private members.
>>
>> Worse yet, the way it is now, there's no way to tell
>> they are marked private when using reflection!
>>
>
> Awful.

As someone who has implemented a runtime reflection library in D, it is entirely possible to detect whether a function is marked private/protected or not using __traits today. In fact, IIRC, there is no way to break protection using __traits; what the op is referring to is .tupleof, which can be used to break protections of fields if you have the full source code.
April 03, 2012
Re: traits getProtection
On Tuesday, 3 April 2012 at 13:14:00 UTC, Robert Jacques wrote:
> As someone who has implemented a runtime reflection library in 
> D, it is entirely possible to detect whether a function is 
> marked private/protected or not using __traits today.

How did you do it? __traits(compiles) is the best I could
find, and that breaks down if you are friends (easy to
happen with mixins, even if the code is in a separate file)
and is kinda fragile in general since it will swallow unrelated
errors too.
April 03, 2012
Re: traits getProtection
On 4/3/12, Adam D. Ruppe <destructionator@gmail.com> wrote:
> is kinda fragile in general since it will swallow unrelated
> errors too.

That's an issue I've noticed recently. msgpack-d allows me to define a
custom serialization routine in my structs/classes, but it has to be a
template. Then msgpack tries to instantiate it via __traits(compiles),
and if it doesn't work it just skips calling the routine alltogether.
So if I have invalid code in my template I'll never know because the
external library just swallows the errors.

It took me a long time to figure out why my routine wasn't called. I
really wish DMD would semantically check templates at least partially
even if they're never instantiated.
April 04, 2012
Re: traits getProtection
On Tue, 03 Apr 2012 08:30:25 -0500, Adam D. Ruppe <destructionator@gmail.com> wrote:

> On Tuesday, 3 April 2012 at 13:14:00 UTC, Robert Jacques wrote:
>> As someone who has implemented a runtime reflection library in
>> D, it is entirely possible to detect whether a function is
>> marked private/protected or not using __traits today.
>
> How did you do it? __traits(compiles) is the best I could
> find, and that breaks down if you are friends (easy to
> happen with mixins, even if the code is in a separate file)
> and is kinda fragile in general since it will swallow unrelated
> errors too.

I did it by having all the inspection routines in a private template inside a struct in another module.
April 04, 2012
Re: traits getProtection
On Tuesday, April 03, 2012 08:23:49 deadalnix wrote:
> Le 02/04/2012 22:59, Simen Kjærås a écrit :
> > On Mon, 02 Apr 2012 20:02:20 +0200, deadalnix <deadalnix@gmail.com> wrote:
> >>> Now, there are a number of people very unhappy about this state of
> >>> affairs and
> >>> want private to hide symbols as well (personally, I think that the
> >>> fact that
> >>> it makes private aliases effectively useless is reason enough to
> >>> seriously
> >>> reconsider the current behavior), but I don't know if there's any
> >>> real chance
> >>> of convincing Walter or not.
> >> 
> >> This would be a huge mistake. For instance, private method are
> >> sometime meant to be overridden in subclasses, which is impossible if
> >> symbol is inaccessible.
> >> 
> >> NVI for instance would be impossible in such a situation.
> > 
> > NVI is perfectly possible with protected.
> 
> You'll loose the ability to define a function, without being able to
> call it.

Except that that doesn't even actually work as discussed in this thread:

http://www.digitalmars.com/d/archives/digitalmars/D/Re_Module-
level_accessibility_118209.html#N118329

The derived class overrode the function, so it can call it. It may not be able 
to call the base class version, but it can call its own.

Sure, NVI is great, but it works just as well with protected. private doesn't 
actually prevent you from calling the function in the derived class, and even 
if it did, it's _not_ worth the cost of making private virtual by default. And 
as D lets the compiler control virtuality, unlike C++, it doesn't make any 
sense to make it so that the programmer can specifically make a private 
function virtual to work with NVI. So, it just makes more sense to use 
protected to do NVI.

Now, it may be different with interfaces. TDPL specifically talks about using 
private for NVI with _interfaces_, not classes. Doing that sort of thing with 
interfaces requires special treatment already, and it doesn't affect efficiency 
like making private always virtual would, so that should be okay. In the 
general case though, it's just far better to use protected to do NVI with 
classes and let private be non-virtual and therefore efficient by default rather 
than inefficient by default.

- Jonathan M Davis
April 04, 2012
Re: traits getProtection
Le 04/04/2012 04:48, Jonathan M Davis a écrit :
> On Tuesday, April 03, 2012 08:23:49 deadalnix wrote:
>> Le 02/04/2012 22:59, Simen Kjærås a écrit :
>>> On Mon, 02 Apr 2012 20:02:20 +0200, deadalnix<deadalnix@gmail.com>  wrote:
>>>>> Now, there are a number of people very unhappy about this state of
>>>>> affairs and
>>>>> want private to hide symbols as well (personally, I think that the
>>>>> fact that
>>>>> it makes private aliases effectively useless is reason enough to
>>>>> seriously
>>>>> reconsider the current behavior), but I don't know if there's any
>>>>> real chance
>>>>> of convincing Walter or not.
>>>>
>>>> This would be a huge mistake. For instance, private method are
>>>> sometime meant to be overridden in subclasses, which is impossible if
>>>> symbol is inaccessible.
>>>>
>>>> NVI for instance would be impossible in such a situation.
>>>
>>> NVI is perfectly possible with protected.
>>
>> You'll loose the ability to define a function, without being able to
>> call it.
>
> Except that that doesn't even actually work as discussed in this thread:
>
> http://www.digitalmars.com/d/archives/digitalmars/D/Re_Module-
> level_accessibility_118209.html#N118329
>
> The derived class overrode the function, so it can call it. It may not be able
> to call the base class version, but it can call its own.
>

It shouldn't be able to do so. This should be reserved for protected 
methods.

> Sure, NVI is great, but it works just as well with protected. private doesn't
> actually prevent you from calling the function in the derived class, and even
> if it did, it's _not_ worth the cost of making private virtual by default. And
> as D lets the compiler control virtuality, unlike C++, it doesn't make any
> sense to make it so that the programmer can specifically make a private
> function virtual to work with NVI. So, it just makes more sense to use
> protected to do NVI.
>

Visibility and virtuality are 2 completely orthogonal concerns. Mixing 
both is a bad design decision, what ever is the rational behind it. 
Separation of concerns is more important.

Plus, this isn't a real issue, because the final keyword exists.

At the end, for performance concerns, what we want is that the compiler 
or the linker were able to finalize methods that have no override, not 
some dirty trick that break larger more important conception principles.

> Now, it may be different with interfaces. TDPL specifically talks about using
> private for NVI with _interfaces_, not classes. Doing that sort of thing with
> interfaces requires special treatment already, and it doesn't affect efficiency
> like making private always virtual would, so that should be okay. In the
> general case though, it's just far better to use protected to do NVI with
> classes and let private be non-virtual and therefore efficient by default rather
> than inefficient by default.
>
> - Jonathan M Davis

It is not that simple. First, it introduce an inconsistency between 
interfaces and classes for no real reasons. The only difference between 
classes and interfaces should be that interface cannot have member data, 
and you can inherit from multiple interfaces. Interface have been 
created to solve the problems that exists for multiple inheritance, and 
that is enough to solve that problem. Everything else is, again, lack of 
separation of concerns.

Second, the same method can be declared in the base class and in an 
interface, and in this case, we cause compile error for nothing.
April 04, 2012
Re: traits getProtection
Le 04/04/2012 03:04, Robert Jacques a écrit :
> On Tue, 03 Apr 2012 08:30:25 -0500, Adam D. Ruppe
> <destructionator@gmail.com> wrote:
>
>> On Tuesday, 3 April 2012 at 13:14:00 UTC, Robert Jacques wrote:
>>> As someone who has implemented a runtime reflection library in
>>> D, it is entirely possible to detect whether a function is
>>> marked private/protected or not using __traits today.
>>
>> How did you do it? __traits(compiles) is the best I could
>> find, and that breaks down if you are friends (easy to
>> happen with mixins, even if the code is in a separate file)
>> and is kinda fragile in general since it will swallow unrelated
>> errors too.
>
> I did it by having all the inspection routines in a private template
> inside a struct in another module.

That is neat.

It should be provided as lib by std.traits . And no need for language 
changes.
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