id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
12135	Boost.Concepts shoudn't create typedefs based on line number	russellgreene8@…	jsiek	"Hey so today I spent about 30 minutes tearing my hair out over this compile error: 

 error: typedef redefinition with different types ('instantiate<&::boost::concepts::requirement_<void (*)(concept::Window<qt_window>)>::failed>' vs 'instantiate<&::boost::concepts::requirement_<void (*)(concept::Viewport<qt_viewport>)>::failed>')

This error isn't useful to what was happening. I had two BOOST_CONCEPT_ASSERT((...))s in two different files, under the global namespace. At first I theorized that it wasn't just supported but according to the docs BOOST_CONCEPT_ASSERT can be used in any scope. Then I started to look at the implementation and found this line:  BOOST_PP_CAT(boost_concept_check,__LINE__) which gave it all away: they were both on the same line. The thing is that I use a code formatter, so I actually have to add comments or code to change the line number a line of code is on. 

I would love this to be fixed. There is a fine workaround, but it isn't a very easy to find error in your code. 

Here is a simple test case. Just add a newline before the BOOST_CONCEPT_ASSERT((...)) in either of the headers to get rid of the error:

{{{
#!div style=""font-size: 80%""
Code highlighting:
  {{{#!C++
// a.h
#include <boost/concept_check.hpp>

BOOST_CONCEPT_ASSERT((boost::Integer<int>)); // note line number
  }}}
}}}


{{{
#!div style=""font-size: 80%""
Code highlighting:
  {{{#!C++
// b.h
#include <boost/concept_check.hpp>

BOOST_CONCEPT_ASSERT((boost::UnsignedInteger<unsigned int>)); // note line number
  }}}
}}}


{{{
#!div style=""font-size: 80%""
Code highlighting:
  {{{#!C++
// main.cpp
#include ""a.h""
#incldue ""b.h""

int main(){}
  }}}
}}}

"	Bugs	new	To Be Determined	concept_check	Boost 1.60.0	Problem		Compile Error