boost::math::tools::promote_args not works with C++23 FP-types

From: Gero Peterhoff (g.peterhoff_at_[hidden])
Date: 2023-02-19 14:48:47

Hi,
promote_args from <boost/math/tools/promotion.hpp> not works with new/extended C++23 FP-types
https://godbolt.org/z/13fq8a3d7


The problem might be the outdated "manual variadic" implementation for C++03. Well, according to the documentation (https://www.boost.org/doc/libs/1_81_0), boost::math requires C++11 anyway; with a switch to C++11 it also works (std::common_type).

This issue also affects some implementations in boost::math::policies.

PS:
We have (at least) 3 different definitions for the *same* boost::float128(_type/_t) type
1) <boost/config.hpp>: boost::float128_type
2) <boost/math/cstdfloat/cstdfloat_types.hpp>/<boost/math/cstdfloat/cstdfloat_cmath.hpp>: BOOST_CSTDFLOAT_FLOAT128_NATIVE_TYPE/float128_t
3) <boost/math/tools/config.hpp>: BOOST_MATH_FLOAT128_TYPE
:-(

thx
Gero