使用gcc 4.7和boost 1.49时,使用以下表达式is_assignable返回true:
typedef boost::function<void()> F;
std::is_assignable<F, std::nullptr_t>::value
但是,此代码无法编译:
boost::function<void()> f;
f = nullptr;
产生以下错误消息:
In file included from c:\mingw\bin\../lib/gcc/i686-pc-mingw32/4.7.0/../../../../include/boost/function/detail/maybe_include.hpp:13:0,
from c:\mingw\bin\../lib/gcc/i686-pc-mingw32/4.7.0/../../../../include/boost/function/detail/function_iterate.hpp:14,
from c:\mingw\bin\../lib/gcc/i686-pc-mingw32/4.7.0/../../../../include/boost/preprocessor/iteration/detail/iter/forward1.hpp:47,
from c:\mingw\bin\../lib/gcc/i686-pc-mingw32/4.7.0/../../../../include/boost/function.hpp:64,
from ..\main.cpp:8:
c:\mingw\bin\../lib/gcc/i686-pc-mingw32/4.7.0/../../../../include/boost/function/function_template.hpp: In instantiation of 'static void boost::detail::function::void_function_obj_invoker0<FunctionObj, R>::invoke(boost::detail::function::function_buffer&) [with FunctionObj = std::nullptr_t; R = void]':
c:\mingw\bin\../lib/gcc/i686-pc-mingw32/4.7.0/../../../../include/boost/function/function_template.hpp:907:60: required from 'void boost::function0<R>::assign_to(Functor) [with Functor = std::nullptr_t; R = void]'
c:\mingw\bin\../lib/gcc/i686-pc-mingw32/4.7.0/../../../../include/boost/function/function_template.hpp:722:7: required from 'boost::function0<R>::function0(Functor, typename boost::enable_if_c<boost::type_traits::ice_not<boost::is_integral<Functor>::value>::value, int>::type) [with Functor = std::nullptr_t; R = void; typename boost::enable_if_c<boost::type_traits::ice_not<boost::is_integral<Functor>::value>::value, int>::type = int]'
c:\mingw\bin\../lib/gcc/i686-pc-mingw32/4.7.0/../../../../include/boost/function/function_template.hpp:1042:16: required …