[Bug c++/50258] [C++0x] -std=gnu++0x should allow in-class initialization of static const floating types without constexpr

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50258

--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-09-29 11:49:09 UTC ---
(In reply to comment #9)
> Even though the proposed patch seems to be a proper solution, to me it seems to
> be that using -fpermissive just to come around this particular error is
> allowing other non-confirming code to compile as well, which may not be desired
> in many situations (for instance, assigning a const pointer to a non-const
> pointer would not be regarded as an error).

Yup. Some compilers allow every single backwards-compatibility feature to be
controlled by a separate option. The cost of developing, testing and
maintaining that is enormous.

> In my case, I have modified the patch to throw a warning instead, but probably
> the best solution would be to add a sort of -fno-constexpr-initialization-check
> flag. I read that the previous GCC extension is deprecated now, but it is
> important to take into account that then it would be hard to use c++11 with
> older code, just because of details like this one.

That older code wasn't valid in C++03 either, and relied on an extension which
was deprecated many years ago.  That sounds like exactly the sort of situation
-fpermissive is for.

Rather than changing the effect on this extension, I'd prefer if -fpermissive
was changed to reject some truly *ancient* features which haven't been
supported without -fpermissive by any version of G++ since 3.0