To C++11 or not?

[Kevin Funk]

On Monday, 14 November 2016 10:45:07 CET Martin Gräßlin wrote:
> Hi framework devs,
> 
> recently we started to see the first patches for frameworks to silence
> warnings for not used features of C++11. In particular to add override
> to methods of inheriting classes.
> 
> Now I find this weird from the perspective of our C++ requirements. On
> the one side we say that we are not allowed to use these features to
> still support non-C++11 compilers on the other side we see that
> compilers already generate warnings if you don't use the C++11 features.
> 
> In that particular case I do not think that Q_DECL_OVERRIDE is a
> solution. It's an ugly hack and for the frameworks I maintain I gave a
> -2 on the review. I think this needs a general solution of either not
> adding or adding override, but not the Qt hack.
> 
> I think this is a sign that we need to move on. We cannot continue with
> the state we are in. It's too much a hassle for developers:
> * false-positive compile warnings
> * no way to check which features are allowed or not
> * no warnings if a not allowed feature is used
> * no CI system in place to ensure our rules
> 
> Given that I want to suggest that we remove all compiler restrictions
> and allow the full feature set of C++11. If someone still thinks we need
> to support the compilers not supporting C++11, I would like to see a
> plan on how we can improve the developer story, especially how to
> address the last two points in my list above.
> 
> Opinions?

Heya,

Following-up on this thread, since I saw some more discussion about C++11 
usage in this RR: 
  https://git.reviewboard.kde.org/r/129724/

Let's put this into some concrete actions, finally. I think we all agree 
nullptr & override are probably the most apparent issues (since compilers 
started to warn about both), and *having* 'override' is actually super useful 
for preventing programmer faults.

Let's just speak about allowing nullptr & override, allowing the full set of C
++11 is *not* feasible. Reason: Lot's of C++11 feature are only available only 
in MSVC2015, so we'd just be able to support the latest VS. See [2].

Looking at [1] I still see we list GCC 4.5 as minimum requirement. That's 
pretty ancient. 4.5.1 got released Jul 2010 [3]

If we raise that to GCC 4.6 (4.6.0 being released Mar 2011), we can use 
'nullptr' unconditionally. ktexteditor already did that in public headers for 
quite some time -- no-one complained.

If we raise that to GCC 4.7 (4.7.0 being released Mar 2012), we can use 
'override' unconditionally *.

We already use MSVC2012 as min VS dep, this version has full nullptr & 
override support. I don't see anyone using MSVC2010 for compiling KF5 to be 
honest...

Proposal for [1]:
- Raise min GCC version to 4.7
- Allow to use override unconditionally
- Allow to use nullptr unconditonally

ACK?


PS: I can do the work, I can script the refactoring with clang-tidy.

Let's move forward please.

Cheers,
Kevin

[1] https://community.kde.org/Frameworks/
Policies#Frameworks_compiler_requirements_and_C.2B.2B11
[2] http://en.cppreference.com/w/cpp/compiler_support
[3] https://gcc.gnu.org/releases.html
[4] https://en.wikipedia.org/wiki/Microsoft_Visual_Studio#History
   
> Cheers
> Martin


-- 
Kevin Funk | kfunk at kde.org | http://kfunk.org
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