如何使用 CRTP 创建少量对象？

Question

我编写了一些小示例 CRTP 模式，以便更好地学习它并在更复杂的代码中使用它。我想使用 CRTP，基 class 可以访问派生 class。好的，但我无法为我的基地创建一些对象 class。如果我首先为两个对象 Base<Derived1> base1; Base<Derived2> base2; 调用构造函数，然后从每个对象 base1.PrintDerived_FromA(); base2.PrintDerived_FromA(); 第二次调用函数，我得到的结果是：

Base constr work
Base constr work
b_: 0
b_: 25

但是，我应该有：

Base constr work
Base constr work
b_: 9
b_: 25

如果我在构造函数之后立即调用函数，一切正常：

Base<Derived1> base1;
base1.PrintDerived_FromA();
Base<Derived2> base2;
base2.PrintDerived_FromA();

结果：

Base constr work
b_: 9
Base constr work
b_: 25

事实证明，新的构造函数调用覆盖了现有对象，但为什么呢？有可能解决这个问题吗？我只想使用 CRTP，没有虚拟功能。

#include <iostream>

template <class T>
class Base {
 public:
  Base();
  void PrintDerived_FromA();
  void InitializeDerived();
};

class Derived1 : public Base<Derived1> {
 public:
  Derived1(int b);
  void PrintDerived();
  void SetDerived(int b);

 private:
  int b_;
};

class Derived2 : public Base<Derived2> {
 public:
  Derived2(int b);
  void PrintDerived();
  void SetDerived(int b);

 private:
  int b_;
};


template <typename T>
Base<T>::Base() {
  InitializeDerived();
  std::cout << "Base constr work" << std::endl;
}

template <>
void Base<Derived1>::InitializeDerived() {
  static_cast<Derived1*>(this)->SetDerived(9);
}

template <>
void Base<Derived2>::InitializeDerived() {
  static_cast<Derived2*>(this)->SetDerived(25);
}

template <typename T>
void Base<T>::PrintDerived_FromA() {
  static_cast<T*>(this)->PrintDerived();
}


Derived1::Derived1(int b) : b_(b), Base() {
  std::cout << "Derived1 constr work" << std::endl;
}

void Derived1::PrintDerived() {
  std::cout << "b_: " << b_ << std::endl;
}

void Derived1::SetDerived(int b) {
  b_ = b;
}


Derived2::Derived2(int b) : b_(b), Base() {
  std::cout << "Derived2 constr work" << std::endl;
}

void Derived2::PrintDerived() {
  std::cout << "b_: " << b_ << std::endl;
}

void Derived2::SetDerived(int b) {
  b_ = b;
}


int main() {
  Base<Derived1> base1;
  Base<Derived2> base2;

  base1.PrintDerived_FromA();
  base2.PrintDerived_FromA();

  return 0;
}

Answer 1

static_cast<Derived1*>(this) 转换无效：this 指向 Base<Derived1> 类型的对象而不是 Derived1。因此取消引用生成的指针会导致未定义的行为。为了使 CRTP 工作，您需要创建派生对象类.

如何使用 CRTP 创建少量对象？

How create few objects with CRTP?

c++

templates

crtp