Re: [boost] [config] BOOST_STATIC_CONSTEXPR in C++11 vs C++14

Subject: Re: [boost] [config] BOOST_STATIC_CONSTEXPR in C++11 vs C++14
From: Gary Furnish (gfurnish_at_[hidden])
Date: 2017-08-22 14:42:44

This seems like a reasonable idea.

On Tue, Aug 22, 2017 at 5:28 AM, Lakshay Garg via Boost
<boost_at_[hidden]> wrote:
> This conversation is in reference to
> https://github.com/boostorg/math/pull/82 but I'm posting it here
> because it might be of interest to some.
>
> On 22 August 2017 at 13:53, jzmaddock <notifications_at_[hidden]> wrote:
>> Note that those changes don't actually make the functions constexpr - or
>> indeed change the way the constants are initialized - in fact in C++14
>> BOOST_STATIC_CONSTEXPR doesn't even imply the constants are "const
>> (C++11 is different, and early implementations prevent you from writing
>> "constexpr const" which is what C++14 permits).
>
> Since BOOST_STATIC_CONSTEXPR behaves differently in C++11 and 14,
> would it be a good idea for boost.config to provide a macro for
> handling the `static const var = ...;` kind of variable
> initializations in a portable manner? Maybe something like
> BOOST_COMPILETIME_CONSTANT?
>
> Such a macro might will be useful for declarations where we want the
> variable to be a constant in all possible senses (compile-time,
> run-time) and allow generating the most optimal code possible with the
> language version, compiler being used in a portable manner.
>
> An example of the kind of constants I am talking about can be seen
> here: https://github.com/boostorg/math/blob/develop/include/boost/math/special_functions/prime.hpp#L40
>
> Lakshay
>
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