问题
Can you see anything wrong with this function declaration?
template<typename... Containers>
std::tuple<typename Containers::value_type...>
foo(const Containers &...args);
When I try to call it, like this:
foo(std::list<int>(), std::vector<float>());
MSVC2013 says error C2027: use of undefined type 'std::tuple<Containers::value_type>
.
I tried rewriting the function declaration with the "late return" syntax and it made no difference.
Is there any way I can achieve what this code is trying to do?
回答1:
You won the right to fill a bug report on microsoft connect… The code is ok on clang and gcc.
A workaround on VS2013 and maybe gcc 4.7 :
template <typename T>
using ValueType = typename T::value_type;
template<typename... Containers>
std::tuple<ValueType<Containers>...>
foo( const Containers &...args ) { return {}; }
来源:https://stackoverflow.com/questions/21607167/dependent-types-with-variadic-templates