[英]Variadic CRTP Base Class with Additional Template Parameters
我有一个特征类,即将在可变参数 CRTP 中使用,以扩展 SmartPointer class 的功能。
这个问题是作为https://stackoverflow.com/a/65373058/5677080的后续问题创建的
一个示例性状 class:
template<typename DERIVED, typename DELETER>
class Owning {
public:
using deleter_type = DELETER;
/* ... */
};
这里是我的 SmartPointer 的实现,这些特征类由可变参数 CRTP 扩展:
template<typename T, template<typename> class POINTER_TRAITS>
class SmartPointer;
template<typename T, template<typename> class POINTER_TRAITS>
struct element_type<SmartPointer<T, POINTER_TRAITS>>
{
using type = T;
};
template<template<typename, typename...> class... TRAITS>
struct make_traits
{
template<typename DERIVED>
struct Traits : public TRAITS<DERIVED>... {};
};
template<typename T, template<typename> class POINTER_TRAITS>
class SmartPointer : public POINTER_TRAITS<SmartPointer<T, POINTER_TRAITS>> {
public:
using pointer = T*;
using element_type = T;
/* ... */
};
最后是类型别名来定义特定的智能指针类型(这里是unique_ptr
)
template<typename T, typename DELETER = DefaultDeleter<T>>
using unique_ptr = SmartPointer<T, make_traits<MoveablePointer, Owning>::template Traits>;
问题是如何将DELETER
模板参数移交给unique_ptr
类型别名中的 Owning class...
我猜是这样的(非工作代码,只是为了展示意图):
template<typename T, typename DELETER = DefaultDeleter<T>>
using unique_ptr = SmartPointer<T, make_traits<MoveablePointer, Owning<DELETER>>::template Traits>;
^^^^^^^^^^^^^^^
沿着这些思路,也许:
template <typename DELETER>
struct MakeOwningWithDeleter {
template <typename T>
using type = Owning<T, DELETER>
};
现在您可以将MakeOwningWithDeleter<DELETER>::type
传递给make_traits
。 您已经用于make_traits
的相同技巧。
template<template<class...>class Z, class...Ts>
struct Partial{
template<class...Us>
using Apply=Z<Ts...,Us...>;
};
然后
template<typename T, typename DELETER = DefaultDeleter<T>>
using unique_ptr = SmartPointer<T, make_traits<MoveablePointer, Partial<Owning,DELETER>::template Apply>::template Traits>;
这确实需要进行此更改:
template<typename DELETER, typename DERIVED>
class Owning {
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