boost的type_traits功能相当强大,特别是function_traits,能够辅助做很多事情。
但是美中不足,function_traits竟然没有针对成员函数做任何的traits提取,似乎有些缺憾。我在boost 1.33基础上修改了boost/type_traits/function_traits.hpp的内容,增强其中的功能,希望能够暂时弥补一下这个遗憾。
以下就直接贴代码了,在Begin of Added by realdodo和End of Added by realdodo之间的就是我的修改了。如果想了解这个function_traits是怎么用的,可以参考 http://www.boost.org/上面的文档。如果想了解原理,那就看看C++ Template里面关于模板偏特化的描述,其实我主要是在做体力活啦。
当然,自己下一个boost用一下、改一下还是最能够说明问题。
//
Copyright 2000 John Maddock (john@johnmaddock.co.uk)
//
Use, modification and distribution are subject to the Boost Software License,
//
Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
//
http://www.boost.org/LICENSE_1_0.txt
).
//
//
See
http://www.boost.org/libs/type_traits
for most recent version including documentation.
#ifndef BOOST_TT_FUNCTION_TRAITS_HPP_INCLUDED
#define
BOOST_TT_FUNCTION_TRAITS_HPP_INCLUDED

#include
<
boost
/
config.hpp
>
#include
<
boost
/
type_traits
/
is_function.hpp
>
#include
<
boost
/
type_traits
/
add_pointer.hpp
>

namespace
boost
{

#ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
namespace detail {

template<typename Function> struct function_traits_helper;

template<typename R>
struct function_traits_helper<R (*)(void)>
{
BOOST_STATIC_CONSTANT(int, arity = 0);
typedef R result_type;
};

template<typename R, typename T1>
struct function_traits_helper<R (*)(T1)>
{
BOOST_STATIC_CONSTANT(int, arity = 1);
typedef R result_type;
typedef T1 arg1_type;
typedef T1 argument_type;
};

template<typename R, typename T1, typename T2>
struct function_traits_helper<R (*)(T1, T2)>
{
BOOST_STATIC_CONSTANT(int, arity = 2);
typedef R result_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T1 first_argument_type;
typedef T2 second_argument_type;
};

template<typename R, typename T1, typename T2, typename T3>
struct function_traits_helper<R (*)(T1, T2, T3)>
{
BOOST_STATIC_CONSTANT(int, arity = 3);
typedef R result_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
};

template<typename R, typename T1, typename T2, typename T3, typename T4>
struct function_traits_helper<R (*)(T1, T2, T3, T4)>
{
BOOST_STATIC_CONSTANT(int, arity = 4);
typedef R result_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
};

template<typename R, typename T1, typename T2, typename T3, typename T4,
typename T5>
struct function_traits_helper<R (*)(T1, T2, T3, T4, T5)>
{
BOOST_STATIC_CONSTANT(int, arity = 5);
typedef R result_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
typedef T5 arg5_type;
};

template<typename R, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6>
struct function_traits_helper<R (*)(T1, T2, T3, T4, T5, T6)>
{
BOOST_STATIC_CONSTANT(int, arity = 6);
typedef R result_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
typedef T5 arg5_type;
typedef T6 arg6_type;
};

template<typename R, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6, typename T7>
struct function_traits_helper<R (*)(T1, T2, T3, T4, T5, T6, T7)>
{
BOOST_STATIC_CONSTANT(int, arity = 7);
typedef R result_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
typedef T5 arg5_type;
typedef T6 arg6_type;
typedef T7 arg7_type;
};

template<typename R, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6, typename T7, typename T8>
struct function_traits_helper<R (*)(T1, T2, T3, T4, T5, T6, T7, T8)>
{
BOOST_STATIC_CONSTANT(int, arity = 8);
typedef R result_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
typedef T5 arg5_type;
typedef T6 arg6_type;
typedef T7 arg7_type;
typedef T8 arg8_type;
};

template<typename R, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6, typename T7, typename T8, typename T9>
struct function_traits_helper<R (*)(T1, T2, T3, T4, T5, T6, T7, T8, T9)>
{
BOOST_STATIC_CONSTANT(int, arity = 9);
typedef R result_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
typedef T5 arg5_type;
typedef T6 arg6_type;
typedef T7 arg7_type;
typedef T8 arg8_type;
typedef T9 arg9_type;
};

template<typename R, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6, typename T7, typename T8, typename T9,
typename T10>
struct function_traits_helper<R (*)(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10)>
{
BOOST_STATIC_CONSTANT(int, arity = 10);
typedef R result_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
typedef T5 arg5_type;
typedef T6 arg6_type;
typedef T7 arg7_type;
typedef T8 arg8_type;
typedef T9 arg9_type;
typedef T10 arg10_type;
};

//
// Begin of Added by realdodo.
//

template <typename R,
typename Parent>
struct function_traits_helper<R (Parent::**)()>
{
BOOST_STATIC_CONSTANT(int, arity = 0);
typedef R result_type;
typedef Parent parent_type;
};

template <typename R,
typename Parent,
typename T1>
struct function_traits_helper<R (Parent::**)(T1)>
{
BOOST_STATIC_CONSTANT(int, arity = 1);
typedef R result_type;
typedef Parent parent_type;
typedef T1 arg1_type;
};

template <typename R,
typename Parent,
typename T1,
typename T2>
struct function_traits_helper<R (Parent::**)(T1, T2)>
{
BOOST_STATIC_CONSTANT(int, arity = 2);
typedef R result_type;
typedef Parent parent_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
};

template <typename R,
typename Parent,
typename T1,
typename T2,
typename T3>
struct function_traits_helper<R (Parent::**)(T1, T2, T3)>
{
BOOST_STATIC_CONSTANT(int, arity = 3);
typedef R result_type;
typedef Parent parent_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
};

template <typename R,
typename Parent,
typename T1,
typename T2,
typename T3,
typename T4>
struct function_traits_helper<R (Parent::**)(T1, T2, T3, T4)>
{
BOOST_STATIC_CONSTANT(int, arity = 4);
typedef R result_type;
typedef Parent parent_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
};

template <typename R,
typename Parent,
typename T1,
typename T2,
typename T3,
typename T4,
typename T5>
struct function_traits_helper<R (Parent::**)(T1, T2, T3, T4, T5)>
{
BOOST_STATIC_CONSTANT(int, arity = 5);
typedef R result_type;
typedef Parent parent_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
typedef T5 arg5_type;
};

template <typename R,
typename Parent,
typename T1,
typename T2,
typename T3,
typename T4,
typename T5,
typename T6>
struct function_traits_helper<R (Parent::**)(T1, T2, T3, T4, T5, T6)>
{
BOOST_STATIC_CONSTANT(int, arity = 6);
typedef R result_type;
typedef Parent parent_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
typedef T5 arg5_type;
typedef T6 arg6_type;
};

template <typename R,
typename Parent,
typename T1,
typename T2,
typename T3,
typename T4,
typename T5,
typename T6,
typename T7>
struct function_traits_helper<R (Parent::**)(T1, T2, T3, T4, T5, T6, T7)>
{
BOOST_STATIC_CONSTANT(int, arity = 7);
typedef R result_type;
typedef Parent parent_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
typedef T5 arg5_type;
typedef T6 arg6_type;
typedef T7 arg7_type;
};

template <typename R,
typename Parent,
typename T1,
typename T2,
typename T3,
typename T4,
typename T5,
typename T6,
typename T7,
typename T8>
struct function_traits_helper<R (Parent::**)(T1, T2, T3, T4, T5, T6, T7, T8)>
{
BOOST_STATIC_CONSTANT(int, arity = 8);
typedef R result_type;
typedef Parent parent_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
typedef T5 arg5_type;
typedef T6 arg6_type;
typedef T7 arg7_type;
typedef T8 arg8_type;
};

template <typename R,
typename Parent,
typename T1,
typename T2,
typename T3,
typename T4,
typename T5,
typename T6,
typename T7,
typename T8,
typename T9>
struct function_traits_helper<R (Parent::**)(T1, T2, T3, T4, T5, T6, T7, T8, T9)>
{
BOOST_STATIC_CONSTANT(int, arity = 9);
typedef R result_type;
typedef Parent parent_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
typedef T5 arg5_type;
typedef T6 arg6_type;
typedef T7 arg7_type;
typedef T8 arg8_type;
typedef T9 arg9_type;
};

template <typename R,
typename Parent,
typename T1,
typename T2,
typename T3,
typename T4,
typename T5,
typename T6,
typename T7,
typename T8,
typename T9,
typename T10>
struct function_traits_helper<R (Parent::**)(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10)>
{
BOOST_STATIC_CONSTANT(int, arity = 10);
typedef R result_type;
typedef Parent parent_type;
typedef T1 arg1_type;
typedef T2 arg2_type;
typedef T3 arg3_type;
typedef T4 arg4_type;
typedef T5 arg5_type;
typedef T6 arg6_type;
typedef T7 arg7_type;
typedef T8 arg8_type;
typedef T9 arg9_type;
typedef T10 arg10_type;
};

//
// End of Added by realdodo.
//

} // end namespace detail

template<typename Function>
struct function_traits :
public detail::function_traits_helper<typename add_pointer<Function>::type>
{
};

#else

namespace detail {

template<int N>
struct type_of_size
{
char elements[N];
};

template<typename R>
type_of_size<1> function_arity_helper(R (*f)());

template<typename R, typename T1>
type_of_size<2> function_arity_helper(R (*f)(T1));

template<typename R, typename T1, typename T2>
type_of_size<3> function_arity_helper(R (*f)(T1, T2));

template<typename R, typename T1, typename T2, typename T3>
type_of_size<4> function_arity_helper(R (*f)(T1, T2, T3));

template<typename R, typename T1, typename T2, typename T3, typename T4>
type_of_size<5> function_arity_helper(R (*f)(T1, T2, T3, T4));

template<typename R, typename T1, typename T2, typename T3, typename T4,
typename T5>
type_of_size<6> function_arity_helper(R (*f)(T1, T2, T3, T4, T5));

template<typename R, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6>
type_of_size<7> function_arity_helper(R (*f)(T1, T2, T3, T4, T5, T6));

template<typename R, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6, typename T7>
type_of_size<8> function_arity_helper(R (*f)(T1, T2, T3, T4, T5, T6, T7));

template<typename R, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6, typename T7, typename T8>
type_of_size<9> function_arity_helper(R (*f)(T1, T2, T3, T4, T5, T6, T7, T8));

template<typename R, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6, typename T7, typename T8, typename T9>
type_of_size<10> function_arity_helper(R (*f)(T1, T2, T3, T4, T5, T6, T7, T8,
T9));

template<typename R, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6, typename T7, typename T8, typename T9,
typename T10>
type_of_size<11> function_arity_helper(R (*f)(T1, T2, T3, T4, T5, T6, T7, T8,
T9, T10));

//
// Begin of Added by realdodo.
//

template<typename R, typename P>
type_of_size<1> function_arity_helper(R (P::*f)());

template<typename R, typename P, typename T1>
type_of_size<2> function_arity_helper(R (P::*f)(T1));

template<typename R, typename P, typename T1, typename T2>
type_of_size<3> function_arity_helper(R (P::*f)(T1, T2));

template<typename R, typename P, typename T1, typename T2, typename T3>
type_of_size<4> function_arity_helper(R (P::*f)(T1, T2, T3));

template<typename R, typename P, typename T1, typename T2, typename T3, typename T4>
type_of_size<5> function_arity_helper(R (P::*f)(T1, T2, T3, T4));

template<typename R, typename P, typename T1, typename T2, typename T3, typename T4,
typename T5>
type_of_size<6> function_arity_helper(R (P::*f)(T1, T2, T3, T4, T5));

template<typename R, typename P, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6>
type_of_size<7> function_arity_helper(R (P::*f)(T1, T2, T3, T4, T5, T6));

template<typename R, typename P, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6, typename T7>
type_of_size<8> function_arity_helper(R (P::*f)(T1, T2, T3, T4, T5, T6, T7));

template<typename R, typename P, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6, typename T7, typename T8>
type_of_size<9> function_arity_helper(R (P::*f)(T1, T2, T3, T4, T5, T6, T7, T8));

template<typename R, typename P, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6, typename T7, typename T8, typename T9>
type_of_size<10> function_arity_helper(R (P::*f)(T1, T2, T3, T4, T5, T6, T7, T8,
T9));

template<typename R, typename P, typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6, typename T7, typename T8, typename T9,
typename T10>
type_of_size<11> function_arity_helper(R (P::*f)(T1, T2, T3, T4, T5, T6, T7, T8,
T9, T10));

//
// End of Added by realdodo.
//

} // end namespace detail

// Won't work with references
template<typename Function>
struct function_traits
{
BOOST_STATIC_CONSTANT(int, arity = (sizeof(detail::function_arity_helper((Function*)0))-1));
};

#endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
}

#endif
//
BOOST_TT_FUNCTION_TRAITS_HPP_INCLUDED
但是美中不足,function_traits竟然没有针对成员函数做任何的traits提取,似乎有些缺憾。我在boost 1.33基础上修改了boost/type_traits/function_traits.hpp的内容,增强其中的功能,希望能够暂时弥补一下这个遗憾。
以下就直接贴代码了,在Begin of Added by realdodo和End of Added by realdodo之间的就是我的修改了。如果想了解这个function_traits是怎么用的,可以参考 http://www.boost.org/上面的文档。如果想了解原理,那就看看C++ Template里面关于模板偏特化的描述,其实我主要是在做体力活啦。
当然,自己下一个boost用一下、改一下还是最能够说明问题。
























































































































































































































































































































































































































































































































