c – 可以使用模板函数std :: async

我试图使用更简单的函数(foo和bar),并发现只有非模板功能正在运行.

#include <algorithm>
#include <future>
#include <string>

void foo(std::string::iterator first,std::string::iterator last)
{
}

template<class BidirectionalIterator>
void bar(BidirectionalIterator first,BidirectionalIterator last)
{
}

int main()
{
    std::string str = "Lorem ipsum,dolor sit amet";

    auto result_reverse = std::async(std::reverse,str.begin(),str.end()); // Compile-time error
    auto result_foo     = std::async(foo,str.end());
    auto result_bar     = std::async(bar,str.end()); // Compile-time error

    result_reverse.get();
    result_foo.get();
    result_bar.get();
}

编译错误如下：

main.cpp: In function ‘int main()’:
main.cpp:18:71: erreur: no matching function for call to ‘async(<unresolved overloaded function type>,std::basic_string<char>::iterator,std::basic_string<char>::iterator)’
main.cpp:18:71: note: candidates are:
/usr/include/c++/4.6/future:1355:5: note: template<class _Fn,class ... _Args> std::future<typename std::result_of<_Functor(_ArgTypes ...)>::type> std::async(std::launch,_Fn&&,_Args&& ...)
/usr/include/c++/4.6/future:1378:5: note: template<class _Fn,class ... _Args> typename std::__async_sfinae_helper<typename std::decay<_Functor>::type,_Fn,_Args ...>::type std::async(_Fn&&,_Args&& ...)
main.cpp:18:71: erreur: unable to deduce ‘auto’ from ‘<expression error>’
main.cpp:20:62: erreur: no matching function for call to ‘async(<unresolved overloaded function type>,std::basic_string<char>::iterator)’
main.cpp:20:62: note: candidates are:
/usr/include/c++/4.6/future:1355:5: note: template<class _Fn,_Args&& ...)
main.cpp:20:62: erreur: unable to deduce ‘auto’ from ‘<expression error>’

但是,当我手动指定模板instanciation,如std :: async(std :: reverse< std :: string :: iterator> str.begin(),str.end())时,它会通过.

这是一个编译器错误(GCC 4.6.3)还是明确的行为？