id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
12874	future<> extension constructor must be under BOOST_THREAD_PROVIDES_FUTURE_UNWRAP	Arthur O'Dwyer	viboes	"In Boost 1.63.0's ""boost/thread/future.hpp"", we see this code:

{{{
    inline explicit BOOST_THREAD_FUTURE(BOOST_THREAD_RV_REF(BOOST_THREAD_FUTURE<BOOST_THREAD_FUTURE<R> >) other); // EXTENSION
}}}

Unfortunately, the actual definition of this inline constructor is located under an #ifdef that may not be defined at compile time:

{{{
#if defined BOOST_THREAD_PROVIDES_FUTURE_UNWRAP
// many lines snipped...
  template <typename R>
  inline BOOST_THREAD_FUTURE<R>::BOOST_THREAD_FUTURE(BOOST_THREAD_RV_REF(BOOST_THREAD_FUTURE<BOOST_THREAD_FUTURE<R> >) other)
  : base_type(other.unwrap()) {}
// several lines snipped...
#endif
}}}

The result is that this inline constructor is declared but not defined, which produces very confusing linker errors.

The appropriate solution is to wrap the declaration of this constructor in

{{{
#if defined BOOST_THREAD_PROVIDES_FUTURE_UNWRAP
#endif
}}}

No other change needs to be made, as far as I know."	Patches	closed	Boost 1.65.0	thread	Boost 1.63.0	Problem	fixed