问题
I have a template struct, which accepts a Iterator type for the template argument. now I need to specialize that class for iterators of different containers. I have tried with std::vector
template<typename Iterator>
struct AC {
};
template<typename T, typename Alloc>
struct AC<typename std::vector<T, Alloc>::iterator> { //this doesn't work
};
but I got this compiler error(VS11): 'T' : template parameter not used or deducible in partial specialization
Can someone please tell me why this doesn't work? And how to make it work?
回答1:
You can't deduce types left of a nesting ::. Indeed, your question makes no sense. Consider this simpler counter-example:
template <typename> struct Foo;
template <> struct Foo<bool> { typedef float type; };
template <> struct Foo<char> { typedef float type; };
template <typename> struct DoesntWork;
template <typename T> struct DoesntWork<typename Foo<T>::type> { };
Now if I say DoesntWork<float>, what should T be?
The point is that there is no reason that any T should exist for which Foo<T>::type is a thing you want to match, and even if there were one, there's no reason why it would be unique.
来源：https://stackoverflow.com/questions/16123279/partial-specialization-for-iterator-type-of-a-specified-container-type