static_assert in arg.hpp failing when using boost::placeholder with std::bind

[anonymous]

In our project we currently use std::bind with boost::placeholers because boost::placeholders are already global namespace and some some of the dependency (header) libraries might depend on this so we can't use BOOST_BIND_NO_PLACEHOLDERS currently.

So we make boost::placeholers work with std::bin with this code:

namespace std {
	template<int N>
	struct is_placeholder<boost::arg<N>> : public integral_constant<int, N> {};
}

This worked fine, but since boost 1.60 when BOOST_CONSTEXPR was added to the boost::arg contructor the compliation fails for some of our developers with

error: static assertion failed: I == is_placeholder<T>::value
         BOOST_STATIC_ASSERT( I == is_placeholder<T>::value );

from arg.hpp

[loonycyborg]

I'm contributor to the same project(namely Battle for Wesnoth), and I got this issue on debian while using mingw-w64 cross toolchain(gcc 4.9). While my gentoo crossdev based cross toolchain(gcc5.3 and the same boost version) compiled same code without errors. atm I'm using 5.3.0 for native builds and not getting this issue there either.

[Peter Dimov]

I'll look into this if someone can present a simple example that triggers the error.

[loonycyborg]

This compiles fine with gcc 5.4.0 but fails with gcc 4.8.5 and 4.9.3, using -std=c++11 option

[Peter Dimov]

Should be fixed in ​https://github.com/boostorg/bind/commit/3c56630b5400c43d1a4393d685a407e68a69ce9e