Functional Programming in C++

Modern compilers required [Activities after 4.9]

Published by Ivan Čukić in the KDE development: Activities section, on 19 May 2012

After the KDE SC 4.9 is released, projects inside KDE Projects: Activities will start requiring more up-to-date compilers and will start (ab)using more modern C++.

For the library, the requirement will be GCC 4.6, clang 3.0 or whatever version of MSVC++ has the equivalent features. GCC 4.6 is chosen since it will be a dependency of Qt 5, so eventually the rest of KDElibs/KDE Frameworks will foolow suit.

Since GCC is the main targeted compiler, the library will be regularly tested against 4.6. For Clang, I’ll test with the latest version provided by Debian (currently 3.0).

With that said, I don’t expect that the library will really be uncompilable with older compilers, it is just that I have no intention keeping the compatibility and testing for it.

Service

For the service, the requirement will be more obvious - compilation will likely fail on older compilers. I’m currently pondering whether to require GCC 4.6 or 4.7. The later has some rather nice additions from C++11 standard (that are present in Clang 3.0) like Non-static data member initializers (N2756), Template aliases (N2258), Delegating constructors (N1986), Explicit virtual overrides (N2928, N3206, N3272).

I guess I’ll start of with 4.6 and see whether it is enough and whether I can live without a few adorable N****s :)

Edit: Regarding kde-core-devel - I will start this discussion on k-c-d once 4.9 is out of the door. The point of this post is to test the public responses. Don’t want to bother everybody on k-c-d for something that is not intended for this release.

Taretti
Why should you care? Just stick with the last version. That will make your life easier and the code will be cleaner, just go for it :)
It's not like you're using beta software... it's stable and it's there, you should use it.
Djuro Drljaca
@Taretti: some operating systems don't support the latest versions of compilers or have a completely different compiler that might not support all the needed features.
Probably they try to be as compatible as possible, so they set a "minimum version" of a compiler...
Ivan Čukić
@<a href="#comment-27274" rel="nofollow">Taretti</a>: Exactly what Djuro said. Some systems don't have up-to-date compilers. For example our MeeGo-based Plasma Active is on 4.5.something.
I've had a bug report on Lancelot a few years ago that it doesn't compile against GCC 3.2 or something. :)
tosky
Shouldn't this require at least a discussion on kde-core-devel@ ?
Ivan Čukić
@<a href="#comment-27278" rel="nofollow">tosky</a>: Of course, currently just testing the public responses - before opening the flood gates on kcd.
Christophe Giboudeaux
Hm... ever heard of the dependency freeze ?
The dependency freeze was on the 10th May and as far as I can see, this wasn't discussed on k.c.d, kde-buildsystem nor the release-team ML.
Ivan Čukić
@<a href="#comment-27283" rel="nofollow">Christophe Giboudeaux</a>: Yes... This is not about 4.9, but for <b>*after*</b> 4.9, which should be clear from the title and the first sentence.
uniq
Please consider using GCC 4.5 as a minimum requirement. I know that the new C++11 features would be handy in many cases, but there are far to many systems out there which do not yet support these. Most main distributions ship 4.6 (openSuse 12.1, Fedora 16, Debian Wheezy, Ubuntu 12.04?) or even 4.5 (like the still supported openSuse 11.4). Debian uses 4.4 in Squeeze. I don't know how the situation is for the BSDs. Most users or their admins are not that update prone as developers.
Ivan Čukić
@<a href="#comment-27294" rel="nofollow">uniq</a>: Main distros have 4.6 either in their current version, or in the next release (where current stable is for minor updates-only so it will not be affected by changing this policy).
FreeBSD 10 seems will be based on clang 3.1 which is as supportive of C++11 as GCC 4.6 or better.
> Most users or their admins are not that update > prone as developers.
Updating a compiler is as easy as updating KDE software, if not more.
As I said Qt 5 will require GCC 4.6, having us depend on anything below that would be a vain effort - we will switch to Qt 5 at some point, so 4.6 will be minimum.
4.5 supports a lot of nice features, but is it sufficient, we'll see.
The User
Good choice to use modern features, prioritising good code instead of minimal dependencies. :)
uniq
@<a href="#comment-27295" rel="nofollow">Ivan Čukić</a>: Ja, I think you are right when you'll request a GCC 4.6. The Qt5 argument is a good one. And when KDE 4.10 will be released, most interested parties probably can gets hands on a newer GCC package.
Kevin Kofler
uniq wrote: > Most main distributions ship 4.6 (openSuse 12.1, Fedora 16, Debian Wheezy, Ubuntu 12.04?)
Fedora 16 will have reached its end of life by the time KDE SC 4.10 will be released (unless some major scheduling changes happen on either end). (Remember this is about KDE SC 4.10, not KDE SC 4.9.) Fedora 17 will ship GCC 4.7.
yokem55
The only major distro that I am aware of that still has a pre gcc-4.6 compiler by default is Gentoo. 4.5.3 is currently the "stable" version of gcc that Gentoo defaults to. Now, gentoo, given the central place the compiler has in the distro, is pretty conservative about gcc upgrades and 4.6 is currently marked as unstable and is hard masked because several packages still don't compile properly with the newer version of gcc. However by the time 4.10 or whatever the post 4.9 release will be, this should be resolved...
Ivan Čukić
@<a href="#comment-27300" rel="nofollow">yokem55</a>: Cool, thanks for the info!