如何在可变参数派生 class 中执行来自 crtp base classes 的所有函数？

Question

我有一个 CRTP 派生的 class，它是它可以继承的所有 CRTP 基础 classes 的可变参数模板。我想在派生的 class（printAll 函数）的方法中从每个继承的 class（在本例中为 print 函数）执行一个函数。我怎样才能做到这一点？

// Base Class 1
template<typename Derived>
struct Mult
{
  void print()
  {
    int a = (static_cast<Derived const&>(*this)).m_a;
    int b = (static_cast<Derived const&>(*this)).m_b;
    std::cout << "a * b: " << a * b << "\n";
  }
};

// Base Class 2
template<typename Derived>
struct Add
{
  void print()
  {
    int a = (static_cast<Derived const&>(*this)).m_a;
    int b = (static_cast<Derived const&>(*this)).m_b;
    std::cout << "a + b: " << a + b << "\n";
  }
};

template<template<typename> typename... Bases>
struct Derived : public Bases<Derived<Bases...>>...
{
  int m_a, m_b;
  Derived(int a, int b) : m_a(a), m_b(b) {}
  void printAll()
  {
    // Should execute the print method of all the derived classes
    this->print();
  }
};


int main()
{
  Derived<Mult, Add> d(2, 3);
  // should print:
  // a + b: 5
  // a * b: 6
  d.printAll();
}

Answer 1

  void printAll()
  {
    auto _ = {(Bases<Derived<Bases...>>::print(), 0) ...};
  }

Demo

Answer 2

您可以使用 fold expression，C++17 中的一项新语言功能：

void printAll()
{
    (Bases<Derived>::print(), ...);
}

如何在可变参数派生 class 中执行来自 crtp base classes 的所有函数？

How to execute all functions from crtp base classes in a variadic derived class?

c++

crtp

variadic-templates

c++17