How to use a templated function as custom predicate for Boost::Unit-test

Question

I am trying to build a custom predicate for BOOST_CHECK_PREDICATE where the predicate itself is a templated function. My example looks as follows:

#define BOOST_TEST_MODULE Module
#define BOOST_TEST_MAIN
#include <boost/test/unit_test.hpp>

// custom predicate
template <typename U, typename V>
bool is_close_enough(const U& a, const V& b)
{
    return std::abs(a-b) < 2.0;
}

BOOST_AUTO_TEST_SUITE(boostUnitTestLearningTests)

BOOST_AUTO_TEST_CASE(Test_Templated_Predicate)
{
    BOOST_CHECK_PREDICATE(is_close_enough, (4)(6));
    BOOST_CHECK_PREDICATE(is_template_close_enough, (4.0)(6.5));
}

BOOST_AUTO_TEST_SUITE_END()

Compiling with MS Visual C++ 2010 gives the following errors:

3>..\boost_test\testSystem.cpp(42): error C2780: 'bool boost::test_tools::tt_detail::check_frwd(Pred,const boost::unit_test::lazy_ostream &,boost::test_tools::const_string,size_t,boost::test_tools::tt_detail::tool_level,boost::test_tools::tt_detail::check_type,const Arg0 &,const char *,const Arg1 &,const char *,const Arg2 &,const char *,const Arg3 &,const char *,const Arg4 &,const char *)' : expects 16 arguments - 10 provided 3>
C:\Boost\include\boost-1_51\boost/test/test_tools.hpp(523) : see declaration of 'boost::test_tools::tt_detail::check_frwd' 3>..\boost_test\testSystem.cpp(42): error C2780: 'bool boost::test_tools::tt_detail::check_frwd(Pred,const boost::unit_test::lazy_ostream &,boost::test_tools::const_string,size_t,boost::test_tools::tt_detail::tool_level,boost::test_tools::tt_detail::check_type,const Arg0 &,const char *,const Arg1 &,const char *,const Arg2 &,const char *,const Arg3 &,const char *)' : expects 14 arguments - 10 provided 3> C:\Boost\include\boost-1_51\boost/test/test_tools.hpp(523) : see declaration of 'boost::test_tools::tt_detail::check_frwd' 3>..\boost_test\testSystem.cpp(42): error C2780: 'bool boost::test_tools::tt_detail::check_frwd(Pred,const boost::unit_test::lazy_ostream &,boost::test_tools::const_string,size_t,boost::test_tools::tt_detail::tool_level,boost::test_tools::tt_detail::check_type,const Arg0 &,const char *,const Arg1 &,const char *,const Arg2 &,const char *)' : expects 12 arguments - 10 provided 3> C:\Boost\include\boost-1_51\boost/test/test_tools.hpp(523) : see declaration of 'boost::test_tools::tt_detail::check_frwd' 3>..\boost_test\testSystem.cpp(42): error C2896: 'bool boost::test_tools::tt_detail::check_frwd(Pred,const boost::unit_test::lazy_ostream &,boost::test_tools::const_string,size_t,boost::test_tools::tt_detail::tool_level,boost::test_tools::tt_detail::check_type,const Arg0 &,const char *,const Arg1 &,const char *)' : cannot use function template 'bool is_close_enough(const U &,const V &)' as a function argument 3> ..\boost_test\testSystem.cpp(18) : see declaration of 'is_close_enough' 3>..\boost_test\testSystem.cpp(42): error C2784: 'bool boost::test_tools::tt_detail::check_frwd(Pred,const boost::unit_test::lazy_ostream &,boost::test_tools::const_string,size_t,boost::test_tools::tt_detail::tool_level,boost::test_tools::tt_detail::check_type,const Arg0 &,const char *,const Arg1 &,const char *)' : could not deduce template argument for 'overloaded function type' from 'overloaded function type' 3>
C:\Boost\include\boost-1_51\boost/test/test_tools.hpp(523) : see declaration of 'boost::test_tools::tt_detail::check_frwd' 3>..\boost_test\testSystem.cpp(42): error C2780: 'bool boost::test_tools::tt_detail::check_frwd(Pred,const boost::unit_test::lazy_ostream &,boost::test_tools::const_string,size_t,boost::test_tools::tt_detail::tool_level,boost::test_tools::tt_detail::check_type,const Arg0 &,const char *)' : expects 8 arguments - 10 provided

Any ideas what I'm doing wrong here?

Answer 1

The following works fine with Boost 1.53.0 on Visual Studio 2012 and g++ 4.8.1. I think that if you want to use a templated function you need to explicitly specify the template parameters. For this reason I prefer the solution with the functor.

#define BOOST_TEST_MODULE Module
#define BOOST_TEST_MAIN
#include <boost/test/unit_test.hpp>


template <typename U, typename V>
bool is_close_enough(const U& a, const V& b)
{
    return std::abs(a-b) < 2.0;
}

struct is_close_enough_functor
{
    template <typename U, typename V>
    bool operator()(const U& a, const V& b) const
    {
        return std::abs(a-b) < 2.0;
    }
};


BOOST_AUTO_TEST_SUITE(boostUnitTestLearningTests)

BOOST_AUTO_TEST_CASE(Test_Templated_Predicate)
{
    BOOST_CHECK_PREDICATE((is_close_enough<int,int>), (4)(6)); //extra parentheses needed to avoid a problem with the comma inside the macro
    BOOST_CHECK_PREDICATE(is_close_enough_functor(), (4)(6));
    BOOST_CHECK_PREDICATE(is_close_enough_functor(), (4.0)(6.5));
}

BOOST_AUTO_TEST_SUITE_END()