c++ - 访问模板参数 T 的嵌套类型，即使 T 是指针

Question

基本结构:

struct Foo{
    typedef int inner_type;
};

template<class T>
struct Bar{
    typename T::inner_type x;
};

主要内容:

Bar<Foo>();  // Compiles OK
Bar<Foo*>(); // Doesn't compile: template T becomes a pointer-to-class and is not a valid class anymore. 

如何解决这个问题？

Answer 1

将 Bar 结构特化为指向 T 类型的指针:

//non-specialized template for generic type T
template<class T>
struct Bar{
    typename T::inner_type x;
};

//specialization for pointer-to-T types
template<class T>
struct Bar<T*>{
    typename T::inner_type x;
};