Please take a look at the following small test code: /* 1 */ #include <boost/assign/list_of.hpp> /* 2 */ #include <boost/type_traits/is_convertible.hpp> /* 3 */ #include <iostream> /* 4 */ /* 5 */ template <class T> /* 6 */ bool test1(T value) { /* 7 */ return boost::is_convertible<T, int>::value; /* 8 */ } /* 9 */ /* 10 */ template <class T> /* 11 */ int test2(T value) { /* 12 */ return static_cast<int>(value); /* 13 */ } /* 14 */ /* 15 */ /* 16 */ void main() { /* 17 */ std::cout << test1(2.0) << ", "; /* 18 */ std::cout << test1("Unconvertible") << ", "; /* 19 */ std::cout << test1(boost::assign::list_of(1)(3)) << ", "; /* 20 */ /* 21 */ std::cout << test2(2.0) << std::endl; /* 22 */ // std::cout << test2(boost::assign::list_of(1)(3)) << std::endl; /* 23 */ } When I try to use is_convertible<T, int>::value, with T being a boost::assign::list_of, it wrongly results in a "true" value. This code compiles on MSVC 8.0, and running it gives the following output: 1, 0, 1, 2 If you uncomment line 22 (i.e., if you *really* try to convert the types), the code will not compile, with an error on line 19: boost-1.33.1\include\boost\assign\list_of.hpp(152) : error C2564: 'int' : a function-style conversion to a built-in type can only take one argument boost-1.33.1\include\boost\assign\list_of.hpp(129) : see reference to function template instantiation 'Container boost::assign_detail::converter<DerivedTAssign>::convert<Container>(const Container *,boost::assign_detail::default_type_tag) const' being compiled with [ Container=int, DerivedTAssign=boost::assign_detail::generic_list<int> ] boost-1.33.1\include\boost\assign\list_of.hpp(336) : see reference to function template instantiation 'Container boost::assign_detail::converter<DerivedTAssign>::convert_to_container<Container>(void) const' being compiled with [ Container=int, DerivedTAssign=boost::assign_detail::generic_list<int> ] boost-1.33.1\include\boost\type_traits\is_convertible.hpp(202) : see reference to function template instantiation 'boost::assign_detail::generic_list<T>::operator Container(void) const<To>' being compiled with [ T=int, Container=int, To=int ] boost-1.33.1\include\boost\type_traits\is_convertible.hpp(228) : see reference to class template instantiation 'boost::detail::is_convertible_basic_impl<From,To>' being compiled with [ From=boost::assign_detail::generic_list<int> &, To=int ] boost-1.33.1\include\boost\type_traits\is_convertible.hpp(302) : see reference to class template instantiation 'boost::detail::is_convertible_impl<From,To>' being compiled with [ From=boost::assign_detail::generic_list<int>, To=int ] boost-1.33.1\include\boost\type_traits\is_convertible.hpp(348) : see reference to class template instantiation 'boost::detail::is_convertible_impl_dispatch<From,To>' being compiled with [ From=boost::assign_detail::generic_list<int>, To=int ] test_is_convertible.cpp(7) : see reference to class template instantiation 'boost::is_convertible<From,To>' being compiled with [ From=boost::assign_detail::generic_list<int>, To=int ] test_is_convertible.cpp(19) : see reference to function template instantiation 'bool test1<boost::assign_detail::generic_list<T>>(boost::assign_detail::generic_list<T>)' being compiled with [ T=int ]