具有依赖范围的嵌套模板

What is dependent scope and what is the meaning of typename in the context of the following error?

$ make
g++ -std=gnu++0x main.cpp
main.cpp:18:10: error: need 'typename' before 'ptrModel<std::vector<Data> >::Type' because 'ptrModel<std::vector<Data> >' is a dependent scope
make: *** [all] Error 1


/*
 * main.cpp
 */

#include <vector>
#include <memory>

template<typename T>
struct ptrModel
{
 typedef std::unique_ptr<T> Type;
};


template<typename Data>
struct ptrType
{
 typedef ptrModel< std::vector<Data> >::Type Type;
};

int main()
{
 return 0;
}

推荐答案

编译器会准确地告诉您要做什么.在ptrModel之前写typename;>::Type，像这样:

 typedef typename ptrModel<std::vector<Data> >::Type Type;