從模板內綁定模板功能

Question

從this question開始的延續。我試圖綁定一個給定的函數，該函數返回一些其他的東西，而不是void，以便稍後可以簡單地調用f（）。但是，以下代碼無法在GCC 4.4上編譯。它在VS 2010上編譯，但由此產生的程序崩潰。

template<typename RetType> 
void _hideRet(std::function<RetType()> func, RetType * ret) 
{ 
    *ret = func(); 
} 

template<typename FuncType, typename RetType, typename ParamType> 
std::function<void()> registerFunc(FuncType func, RetType * ret, ParamType param) 
{ 
    auto f = std::bind(func, std::forward<ParamType>(param)); 
    return std::bind(_hideRet<RetType>, f, ret); 
} 

int myFunction(std::string text) 
{ 
    std::cout << text << std::endl; 
    return 42; 
} 

int main() 
{ 
    int ret = 0; 
    auto f = registerFunc(myFunction, &ret, "text"); 
    f(); 
    std::cout << ret << std::endl; 
    return 0; 
} 

GCC產生這種瘋狂的消息：

In file included from /usr/include/c++/4.4/functional:70, 
       from func.cpp:4: 
/usr/include/c++/4.4/tr1_impl/functional: In member function ‘typename std::result_of<_Functor(typename std::result_of<std::_Mu<_Bound_args, std::is_bind_expression::value, (std::is_placeholder::value > 0)>(_Bound_args, std::tuple<_UElements ...>)>::type ...)>::type std::_Bind<_Functor(_Bound_args ...)>::__call(const std::tuple<_UElements ...>&, std::_Index_tuple<_Indexes ...>) [with _Args = , int ..._Indexes = 0, 1, _Functor = void (*)(std::function<int()>, int*), _Bound_args = std::_Bind<int (*(const char*))(std::string)>, int*]’: 
/usr/include/c++/4.4/tr1_impl/functional:1191: instantiated from ‘typename std::result_of<_Functor(typename std::result_of<std::_Mu<_Bound_args, std::is_bind_expression::value, (std::is_placeholder::value > 0)>(_Bound_args, std::tuple<_UElements ...>)>::type ...)>::type std::_Bind<_Functor(_Bound_args ...)>::operator()(_Args& ...) [with _Args = , _Functor = void (*)(std::function<int()>, int*), _Bound_args = std::_Bind<int (*(const char*))(std::string)>, int*]’ 
/usr/include/c++/4.4/tr1_impl/functional:1668: instantiated from ‘static void std::_Function_handler<void(_ArgTypes ...), _Functor>::_M_invoke(const std::_Any_data&, _ArgTypes ...) [with _Functor = std::_Bind<void (*(std::_Bind<int (*(const char*))(std::string)>, int*))(std::function<int()>, int*)>, _ArgTypes = ]’ 
/usr/include/c++/4.4/tr1_impl/functional:2005: instantiated from ‘std::function<_Res(_ArgTypes ...)>::function(_Functor, typename __gnu_cxx::__enable_if<(! std::is_integral::value), std::function<_Res(_ArgTypes ...)>::_Useless>::__type) [with _Functor = std::_Bind<void (*(std::_Bind<int (*(const char*))(std::string)>, int*))(std::function<int()>, int*)>, _Res = void, _ArgTypes = ]’ 
func.cpp:16: instantiated from ‘std::function<void()> registerFunc(FuncType, RetType*, ParamType) [with FuncType = int (*)(std::string), RetType = int, ParamType = const char*]’ 
func.cpp:28: instantiated from here 
/usr/include/c++/4.4/tr1_impl/functional:1137: error: invalid conversion from ‘int’ to ‘std::_M_clear_type*’ 
/usr/include/c++/4.4/tr1_impl/functional:1137: error: initializing argument 1 of ‘std::function<_Res(_ArgTypes ...)>::function(std::_M_clear_type*) [with _Res = int, _ArgTypes = ]’ 

我沒有內部STL運作的足夠的知識來做出什麼出格的那個。

但同時實驗，我發現，如果我從registerFunc模板中刪除第二std::bind調用是這樣的：

template<typename FuncType, typename RetType, typename ParamType> 
std::function<RetType()> registerFunc(FuncType func, RetType *, ParamType param) 
{ 
    return std::bind(func, std::forward<ParamType>(param)); 
} 

// in main 
auto tmp = registerFunc(myFunction, &ret, "text"); 
auto f = std::bind(_hideRet<int>, tmp, &ret); 
f(); 

的代碼工作無論是在VS和海灣合作委員會的預期。所以我的結論是，問題是在模板函數中調用std::bind(_hideRet<RetType>, ...)。問題是爲什麼這是一個問題？更重要的是如何解決這個問題？

Answer 1

這絕對是驚人的，但取代：Visual Studio 2010和中運行正常（這基本上是你沒有通過移動第二bind出registerFunc什麼下

std::function<RetType()> f = std::bind(func, std::forward<ParamType>(param)); 
return std::bind(_hideRet<RetType>, f, ret); 

：

auto f = std::bind(func, std::forward<ParamType>(param)); 
return std::bind(_hideRet<RetType>, f, ret); 

通過）。我試圖理解它，但在那之前，這似乎是你的問題的解決方法，