[Kmymoney-devel] KMyMoney Dependencies and Build Requirements

[Cristian Oneț]

2014-10-23 12:38 GMT+03:00 Cristian Oneț <onet.cristian at gmail.com>:
> 2014-07-03 16:32 GMT+03:00 Christian Dávid <christian-david at web.de>:
>> Am Mittwoch, 2. Juli 2014, 21:43:29 schrieb Fernando Vilas:
>>> I think I remember reading that for either Qt5 or KF5, that C++11 was a
>>> requirement. Even as far back as RHEL5, you could get the gcc44 toolchain
>>> installed and use "-std=c++0x" for most of what they use. Based on the
>>> state  of affairs with GCC, LLVM, and MSVC, I have no problem with c++11
>>> being a requirement. This is further supported if I am remembering
>>> correctly above.
>>
>> Both, Qt5 and KF5 do not require C++11. I do not about KF5, but Qt5 has C++11
>> support. If you build it with C++11 enabled some classes contain constexpr,
>> move constructors, initialization lists and other nice improvements.
>>
>> But I do not know if we can make use of it, as the distributions decide if the
>> shared libraries are compiled with C++11 enabled or not.
>>
>> Anyway we should enable C++11 because *we* can make our lives easier with it.
>> I am sure KF5 will require it in near future (Qt probably not). Also I want it
>> enabled because it is more fun for me :)
>>
>> With the compilers you are right, most features are supported by the main
>> compilers for all systems (gcc, clang and MS Visual Studio) for a long time.
>>
>> Also I think it is questionable if someone who has a distribution which is
>> several years old is interested in compiling a new (and quite untested)
>> version of KMyMoney — which will be released at the end of 2014. She/he needs
>> to compile huge packages like Qt5, KF5 and further dependencies as well. Who
>> is willing to do that cannot be stopped with an old compiler.
>
> I've started to do some profiling again and found another argument for
> the case that enabling C++11 would be a great benefit to the project.
>
> 1. We could really benefit from move semantics, our API is a perfect
> fit for that (think about all the MyMoney* objects)
> For example while loading a file the method which takes most CPU
> cycles in the file storage object is MyMoneySeqAccessMgr::price [1].
> You might ask why is that, well... read [2] (I know it's long) and
> you'll notice that the compiler can't perform RVO [3]. We need to
> improve the performance of the code we write but we should not
> sacrifice the readability to do this. We can fix stuff using our
> current C++03 but to do it properly without hurting readability I
> would suggest switching to C++11.

More about this. Since MyMoneyFile return several const objects by
value (not const references) [1] it basically forces a copy of the
temporary in the caller code. I think as a first step we should remove
all const qualifiers from temporary values to allow compilers to
perform optimizations and skip copying.

Regards,
Cristian

[1] https://projects.kde.org/projects/extragear/office/kmymoney/repository/revisions/master/entry/kmymoney/mymoney/mymoneyfile.h#L1251

>
> 2. We could benefit from auto, range-based for and other stuff to
> improve readability
> Line like [4] would simply go away.
>
> 3. It would allow us (the developers) to learn new stuff and write better code
> Although I'm a C++ developer I didn't write a single line of C++11
> code yet. We should be learning and having fun while working in our
> free time.
>
> So, I totally agree with you Chris, let's enable C++11 in KMyMoney, I
> know that KDevelop already needs C++11 so it shouldn't restrict us
> from distributing KMyMoney in any way. I'll take care of the necessary
> build system changes.
>
> Regards,
> Cristian
>
> [1] https://projects.kde.org/projects/extragear/office/kmymoney/repository/revisions/master/entry/kmymoney/mymoney/storage/mymoneyseqaccessmgr.cpp#L1773
> [2] http://www.drdobbs.com/move-constructors/184403855
> [3] http://en.wikipedia.org/wiki/Return_value_optimization
> [4] https://projects.kde.org/projects/extragear/office/kmymoney/repository/revisions/master/entry/kmymoney/mymoney/storage/mymoneyseqaccessmgr.cpp#L1568
>
>>
>> Greetings
>> Chris
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