[cfe-commits] [Patch][Review] constexpr-ification of <limits> and random number generators

[Jonathan Sauer]

Hello,

>> the attached patch constexpr-ifies <limits> as specified in FDIS as well as removes the
>> workarounds in libc++'s random number generators due to missing constexpr (the workarounds
>> don't work when using a non-standard PRNG). The corresponding tests are modified as well.
>> 
>> Please review and, if ok, commit.
>> 
>> 
>> With many thanks in advance,
>> Jonathan
> 
> Thanks Jonathan.  I've been meaning to take care of this.  The current libc++ is a mess with respect to constexpr.
> 
> One of the things I want to do is to allow libc++ to emulate correct behavior even when it is compiled in C++03 mode.  And I don't believe this patch will do this.

No, it indeed does not. As libc++ currently uses said hack in <__config>, I simply worked from there.
I was not aware of the desired C++03 backwards compatibility. BTW, are new C++11 headers supposed to be
backwards compatible, too?

> [...]
> This is just wrong, but taking it out is going to take a little more work.  I haven't nailed down exactly how we want to support both C++03 and C++11 mode, but I'm imagining something similar to the way we're handling noexcept:
> 
> #ifndef _LIBCPP_HAS_NO_CONSTEXPR
> #define _CONSTEXPR_1 constexpr
> #define _CONSTEXPR_0 constexpr
> #else
> #define _CONSTEXPR_1 const
> #define _CONSTEXPR_0
> #endif
> 
> (better macro names would be great!)

How about _CONSTEXPR_FUNC for a constexpr function/method and _CONSTEXPR_STATIC for a constexpr static
member constant:

#ifndef _LIBCPP_HAS_NO_CONSTEXPR
#define _CONSTEXPR_STATIC static constexpr
#define _CONSTEXPR_FUNC constexpr
#else
#define _CONSTEXPR_STATIC static const
#define _CONSTEXPR_FUNC
#endif

I took the liberty of trying this out with <limits>; the patch is attached (I did not touch <random> this
time).


Jonathan
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