id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
6555	output_test_stream does not play nicely with std::ref() (GCC 4.6.1, C++2011 mode)	greenc@…	Gennadiy Rozental	"Under GCC 4.6.1 with Boost 1.48.0 and C++2011 turned on (as it was for the compile of Boost), the following code fails to compile (with appropriate wrapping):

{{{#!C++
boost::test_tools::output_test_stream os;
(void) std::ref(os);
}}}

The relevant part of the error message is (I believe):

{{{
.../include/boost/test/output_test_stream.hpp:42:37: error: 'typedef class boost::test_tools::predicate_result boost::test_tools::output_test_stream::result_type' is private
.../bin/../lib/gcc/x86_64-unknown-linux-gnu/4.6.1/../../../../include/c++/4.6.1/functional:74:46: error: within this context
}}}

It seems that the GCC `std::ref()` function is trying to pick out a nested `result_type` if defined in order to ascertain whether `output_test_stream` is callable. Unfortunately `result_type` is defined but private, which causes a compile error in the template code. 

Solutions:

(1) Use `predicate_result` directly instead of using a typedef at all.

(2) Make the typedef public (may cause problems based on what `std::ref()` does next when it '''does''' think output_test_stream is callable).

(3) Call it something other than `result_type`.

Thanks for your help."	Bugs	closed	To Be Determined	test	Boost 1.48.0	Problem	fixed	C++2011