当涉及到类型推断和管理时， C++11包含大量出色的功能。例如auto和decltype -keywords 已被证明是该语言的一个有价值的补充。
当我采用这些简单而有效的特性时，我开始考虑实现某种反射系统。这是我到目前为止所取得的成果：
/// ------------------------------------------------------------
/// @class Reflection
/// @brief General-purpose reflection class.
/// @exmpl Get type id:
/// auto a = Reflection::get_id_type<int>();
/// auto b = Reflection::get_id_type<Object>();
/// Get type via received id:
/// decltype(Reflection::get_type(a)) d;
/// @note It is forbidden to create an instance of this class.
/// ------------------------------------------------------------
class Reflection{
public:
/// Static member functions:
template<typename T>
static inline long get_id_type(void){
return reinterpret_cast<long>(&Database<T>::id);
}
static auto get_type(long const type_id) -> decltype(/* UNFINISHED! */){ // This is where I'm having problems.
// This function body is intentionally left empty.
// All that matters is the return type.
}
private:
/// Inner structures:
template<typename T>
struct Database{
static void* id; // Created void pointer here, because only the address of this variable matters.
};
/// Constructors & destructors:
Reflection(void) = delete;
~Reflection(void) = delete;
/// Member functions (overloaded operators):
Reflection& operator=(Reflection&&) = delete;
Reflection& operator=(Reflection const&) = delete;
};
代码应该足够容易理解。如果您阅读带有注释的整体代码，您应该知道如何使用这个类。但问题是：
“如何从函数“get_type”返回一个表达式，以便通过decltype -specifier 将此表达式转换为可用类型？
提前致谢。