RFC: Move to C++14

Daniel van Vugt daniel.van.vugt at canonical.com
Wed Feb 18 04:43:21 UTC 2015

As a compromise why don't we say Mir supports the latest LTS only?

So 14 months from now, we'll be free to jump to C++14 (and it will be 
more mature in implementation by then). But until then, we would stick 
to C++11 for trusty.

On 18/02/15 09:39, Daniel van Vugt wrote:
> I think this is a bad idea.
> Supporting trusty with the latest Mir is presently easy, as demonstrated:
> https://code.launchpad.net/~vanvugt/mir/revive-trusty/+merge/249789
> Using newer language specs I think is contrary to engineering maturity.
> Because it means we knowingly and needlessly reduce the number of
> distros Mir can support. And we also make the learning curve for people
> even steeper (fewer C++ developers know the new language features).
> Overall this will lead to reduced adoption by users and reduced
> participation by developers. We need to be careful and draw the line
> somewhere... stop upgrading to the latest C++ every time one comes along.
> - Daniel
> On 17/02/15 20:37, Alexandros Frantzis wrote:
>> Hi all,
>> I think it's to time to consider moving from C++11 to C++14 (at least
>> the C++14 features our compilers support). C++14 offers some useful
>> improvements over C++11, like:
>> * std::make_unique()
>> * standard literal suffixes for std::chrono (e.g. auto delay = 10ms;)
>> * std::shared_timed_mutex (aka RW mutex)
>> * generic lambdas
>> * lambda capture initializers (which, importantly, allow moving values
>> into
>>    lambdas)
>> Moving to C++14 means that we will not be able to build Mir on a
>> pristine Ubuntu LTS 14.04 system. Note that, even now, Mir cannot be
>> fully built on the LTS because of changes in the Android interfaces. As
>> things currently stand, I believe that dropping support for 14.04 builds
>> in order to allow C++14 is a worthy trade-off.
>> In addition, not supporting 14.04 builds means that we will be able to
>> use all the new features of other libraries we depend on, e.g.
>> gmock/gtest.
>> It's also worth noting that our packages depend on g++-4.9 (which
>> supports the C++14 features we want).
>> I have published an MP introducing C++14 into our codebase:
>> https://code.launchpad.net/~afrantzis/mir/introduce-c++14/+merge/249988
>> Let me know what you think.
>> Thanks,
>> Alexandros

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