[Boost-bugs] [Boost C++ Libraries] #6555: output_test_stream does not play nicely with std::ref() (GCC 4.6.1, C++2011 mode)

Subject: [Boost-bugs] [Boost C++ Libraries] #6555: output_test_stream does not play nicely with std::ref() (GCC 4.6.1, C++2011 mode)
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-02-13 23:15:06

#6555: output_test_stream does not play nicely with std::ref() (GCC 4.6.1, C++2011
mode)
------------------------------+---------------------------------------------
 Reporter:  greenc@…          |       Owner:  rogeeff
     Type:  Bugs              |      Status:  new    
Milestone:  To Be Determined  |   Component:  test   
  Version:  Boost 1.48.0      |    Severity:  Problem
 Keywords:  C++2011           |  
------------------------------+---------------------------------------------
 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.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/6555>
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