CONSTEXPR macro (was "Re: [PATCH 1/2] Add OVERRIDE and FINAL macros to coretypes.h")

[David Malcolm <dmalcolm at redhat dot com>]

On Fri, 2016-05-06 at 18:20 +0200, Jakub Jelinek wrote:
> On Fri, May 06, 2016 at 12:40:45PM -0400, David Malcolm wrote:
> > C++11 adds the ability to add "override" after an implementation of
> > a
> > virtual function in a subclass, to:
> > (A) document that this is an override of a virtual function
> > (B) allow the compiler to issue a warning if it isn't (e.g. a
> > mismatch
> > of the type signature).
> > 
> > Similarly, it allows us to add a "final" to indicate that no
> > subclass
> > may subsequently override the vfunc.
> > 
> > We use virtual functions in a few places (e.g. in the jit), so it
> > would
> > be good to get this extra checking.
> > 
> > This patch adds OVERRIDE and FINAL as macros to coretypes.h
> > allowing us to get this extra checking when compiling with a
> > compiler
> > that implements C++11 or later (e.g. gcc 6 by default),
> > but without requiring C++11.
> 
> Don't we also want CONSTEXPR similarly defined to constexpr for C++11
> and
> above and nothing otherwise?

Perhaps, but CONSTEXPR seems to be more awkward than OVERRIDE and
FINAL.  The meanings of "final" and "override" are consistent between
C++11 and C++14, but C++14 allows more things to be marked as
"constexpr" than C++11.  Hence having a single "CONSTEXPR" macro might
not be sufficient.  Perhaps there'd be CONSTEXPR_11 and CONSTEXPR_14
macros for things that are constexpr in C++11 onwards and constexpr in
C++14 onwards, respectively? (seems ugly to me).

Are the OVERRIDE and FINAL macros OK for trunk?

Thanks
Dave