[vtk-developers] vtk-developers Digest, Vol 158, Issue 21

Sun Jun 25 05:50:17 EDT 2017

2017-06-25 11:13 GMT+02:00 Andrew Maclean <andrew.amaclean at gmail.com>:
> This table may be useful to see what features are supported:
> http://en.cppreference.com/w/cpp/compiler_support
>
> Please also remember that we need to ensure that the VTK7.x series are also
> supported, not just VTK8+.

Right, nothing in the code would be changed except initializations on
the form vtkSmartPointer<Type> var = vtkSmartPointer<Type>.

Looks like auto has been supported in all major compilers since 2010.

Elvis

>
> Personally I have no problems with new submissions using C++11 features.
>
> Andrew Maclean
>
> On 25 Jun 2017 18:43, "Elvis Stansvik" <elvis.stansvik at orexplore.com> wrote:
>>
>> But, going back to my original proposal now.
>>
>> 1. Using auto -> not a good idea since people may want to compile with
>> older compilers
>> 2. Using vtkNew -> not a good idea since all the .Get() / .GetPointer()
>> are ugly
>> 3. Tidying up variable names (e.g. "iren", "renWin", ...) -> I got
>> some opposition to that too
>>
>> So I guess I'll hold off on doing anything for now.
>>
>> Though re. 1, what compilers don't support C++11 nowadays? I
>> personally think that would be sufficiently rare at this point that
>> those users could adapt the examples to fit their old compiler.
>>
>> But I guess the bigger question is whether the examples should be
>> curated at all, or always left intact, to not discourage contribution?
>>
>> Elvis
>>
>> 2017-06-25 10:27 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>> > 2017-06-24 22:07 GMT+02:00 Andras Lasso <lasso at queensu.ca>:
>> >> It is great that you've brought this up! There is a very important,
>> >> fundamental difference. Unlike std::shared_ptr or QSharedPointer, VTK smart
>> >> pointer does NOT need clear distinction between the pointer object and the
>> >> raw pointer it holds, because reference counting is implemented in the
>> >> managed object itself.
>> >>
>> >> See in std::shared_ptr documentation: "Constructing a new shared_ptr
>> >> using the raw underlying pointer owned by another shared_ptr leads to
>> >> undefined behavior." (http://en.cppreference.com/w/cpp/memory/shared_ptr)
>> >>
>> >> In VTK, if you assign a vtkSmartPointer to another, internally the raw
>> >> pointer is retrieved and used (Common/Core/vtkSmartPointer.h):
>> >>
>> >>   vtkSmartPointer& operator=(const vtkSmartPointer<U>& r)
>> >>   {
>> >>     this->vtkSmartPointerBase::operator=(CheckType(r.GetPointer()));
>> >>     return *this;
>> >>   }
>> >>
>> >> VTK smart pointers work differently from STL and Qt, so it is
>> >> reasonable to use a different API that reflects this difference. As VTK
>> >> allows safe use of a simpler API, we should take advantage of that and use
>> >> it.
>> >
>> > That's a good point, and an important difference.
>> >
>> > Though, it's still unsafe (of course) in VTK to do say (pseudo):
>> >
>> > struct MyClass {
>> >     void setArray(vtkDataArray *arr) { a = arr; }
>> >     void doSomething() { /* Use the a member here */ }
>> >
>> >     vtkDataArray *a;
>> > }
>> >
>> > and then
>> >
>> > MyClass c;
>> >
>> > { // some scope somewhere
>> >     vtkNew<vtkDataArray> a;
>> >     ...
>> >     c.func(a);
>> > } // a dies (internal pointer freed), c survives
>> >
>> > c.doSomething(); // oops
>> >
>> > But I guess this should be filed in the 'so stupid the user should not
>> > be "protected" from it by a slightly awkward .Get()' category.
>> >
>> > I think you have my vote to add implicit conversion as well.
>> >
>> > Elvis
>> >
>> >>
>> >> Andras
>> >>
>> >> -----Original Message-----
>> >> From: Elvis Stansvik [mailto:elvis.stansvik at orexplore.com]
>> >> Sent: Saturday, June 24, 2017 12:36 PM
>> >> To: Andras Lasso <lasso at queensu.ca>
>> >> Cc: David Lonie <david.lonie at kitware.com>; Shawn Waldon
>> >> <shawn.waldon at kitware.com>; VTK Developers <vtk-developers at vtk.org>; Andrew
>> >> Maclean <andrew.amaclean at gmail.com>
>> >> Subject: Re: [vtk-developers] vtk-developers Digest, Vol 158, Issue 21
>> >>
>> >> 2017-06-24 15:53 GMT+02:00 Andras Lasso <lasso at queensu.ca>:
>> >>> Based on the feedbacks and the poll results (11 out of 13 votes for
>> >>> changing current behavior), it seems there is a strong consensus for
>> >>> adding implicit conversion.
>> >>
>> >> I was away and missed the vote, but frankly I'm not sure what I would
>> >> have voted.
>> >>
>> >> Looking at what others do, I guess vtkNew is comparable to
>> >> std::unique_ptr or Qt's QScopedPointer, none of which do implicit conversion
>> >> to the underlying pointer (they have .get() and .data() respectively). So
>> >> VTK would be rather unique in doing that for a scoped smart pointer I
>> >> think..
>> >>
>> >> Elvis
>> >>
>> >>>
>> >>> Here is a pull request with the change:
>> >>> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitla
>> >>> b.kitware.com%2Fvtk%2Fvtk%2Fmerge_requests%2F2961&data=02%7C01%7Classo
>> >>> %40queensu.ca%7C14c5314b70e443f5be4908d4bb1f0bf4%7Cd61ecb3b38b142d582c
>> >>> 4efb2838b925c%7C1%7C0%7C636339189405346369&sdata=2Jv0QS1qlRUgSJvN%2BO8
>> >>> 0pXOt89kKC0NP7iXXRr2mg30%3D&reserved=0
>> >>>
>> >>> Andras
>> >>>
>> >>> -----Original Message-----
>> >>> From: David Lonie [mailto:david.lonie at kitware.com]
>> >>> Sent: Friday, June 23, 2017 1:51 PM
>> >>> To: Shawn Waldon <shawn.waldon at kitware.com>
>> >>> Cc: Andras Lasso <lasso at queensu.ca>; VTK Developers
>> >>> <vtk-developers at vtk.org>; Andrew Maclean <andrew.amaclean at gmail.com>
>> >>> Subject: Re: [vtk-developers] vtk-developers Digest, Vol 158, Issue 21
>> >>>
>> >>> I'm so glad someone brought this up =)
>> >>>
>> >>> On Fri, Jun 23, 2017 at 10:52 AM, Shawn Waldon
>> >>> <shawn.waldon at kitware.com> wrote:
>> >>>>  But realistically what it does is
>> >>>> discourage use of vtkNew.  Most people I talk to say "I would use
>> >>>> vtkNew but then I have to clutter up my code with GetPointer calls
>> >>>> everywhere" and so they still use vtkSmartPointer.  Honestly I only
>> >>>> used it to clean up declarations (the problem discussed earlier in
>> >>>> this thread).  Now that we can use auto in VTK, I'll probably go back
>> >>>> to vtkSmartPointer since it is easier to use.
>> >>>
>> >>> I agree with Shawn. It's an unnecessary hassle to require the Get() to
>> >>> be used.
>> >>>
>> >>> I suppose I'm just a fan of the design philosophy for C++ about "don't
>> >>> prevent developers from shooting themselves in the foot." If a dev doesn't
>> >>> understand VTK's reference counting well enough to understand that you can't
>> >>> simply return a vtkNew'd pointer without increfing it first, they're going
>> >>> to have far greater problems using the toolkit than this.
>> >>>
>> >>> Besides, you could easily (and safely) return a vtkNew'd pointer from
>> >>> a function:
>> >>>
>> >>> vtkObject* function()
>> >>> {
>> >>>   vtkNew<vtkObject> obj;
>> >>>   obj->Register();
>> >>>   return obj; // If we had implicit conversions, anyway }
>> >>>
>> >>> Making the class unwieldly simply so that people don't need to learn
>> >>> how reference counts work is a poor justification IMO.
>> >>>
>> >>> Just my 2c,
>> >>> Dave
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