ostream& operator<< overload no longer picked up by boost log

[dd0t@…]

Boost log does no longer seem to reliably pick up custom stream operators in boost 1.59.0 (tested with vc14 and vc12). In the example given below the custom operator works fine for cout but isn't found when trying to use it normally for logging. The operator is however found if something else is piped in first. Compiling the same example with 1.58.0 (only tested with vc12) works as expected.

#include <iostream>
#include <ostream>
#include <boost/log/trivial.hpp>

struct Mine {};

std::ostream& operator << (std::ostream& t, const Mine& m) {
	t << "Works";
	return t;
};

int main() {
	Mine m;
	std::cout << m << std::endl; // Works
	BOOST_LOG_TRIVIAL(warning) << m; // error C2678: binary '<<': no operator found which takes a left-hand operand of type 'boost::log::v2s_mt_nt5::basic_record_ostream<char>' (or there is no acceptable conversion)
	BOOST_LOG_TRIVIAL(warning) << "" << m; // Works
	return 0;
};

[Alexander Filonov <kingsbfs@…>]

This also breaks all logging whenever boost::format is used for record formatting. On MVC12 compiler I get the following error:

error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'boost::basic_format<char,std::char_traits<char>,std::allocator<char>>' (or there is no acceptable conversion)

as a temporary solution I redefined my log macro to add an extra empty string:

#define LOG(lg,sev) BOOST_LOG_SEV(lg, sev) << ""

[Andrey Semashev]

Fixed in ​https://github.com/boostorg/log/commit/7da193fde1a9c1bc925ee980339f4df2e1a66fa7. Thanks for the report.