具有附加模板参数的可变 CRTP 基础 Class

Question

我有一个特征 classes，即将在可变 CRTP 中使用它来扩展 SmartPointer 的功能 class。

此问题是

的后续问题

示例特征 class:

template<typename DERIVED, typename DELETER>
class Owning { 
public:
    using deleter_type = DELETER;
    
    /* ... */
};

这是我的 SmartPointer 的实现，它正在通过可变 CRTP 的那些特征进行扩展 classes:

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模板参数交给Owning class in unique_ptr类型别名...

我猜是这样的（非工作代码，只是为了证明意图）：

template<typename T, typename DELETER = DefaultDeleter<T>>
using unique_ptr = SmartPointer<T, make_traits<MoveablePointer, Owning<DELETER>>::template Traits>;
                                                                ^^^^^^^^^^^^^^^

Answer 1

大概是这样的：

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。您已经在 make_traits.

中使用了相同的技巧

Answer 2

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>;

这确实需要进行以下更改：

template<typename DELETER, typename DERIVED>
class Owning {

具有附加模板参数的可变 CRTP 基础 Class

Variadic CRTP Base Class with Additional Template Parameters

c++

variadic-templates

c++20

crtp