`在[模板类] [成员]的实例化中受到保护[。 。 。] [公共成员]无法访问＆＃39;

Question

尝试实例化SystemBody或AcceleratedBody类时遇到以下错误：

error: 'bool InitializationChecker::is_initialized_' is protected

确实，is_initialized_ 是 protected。

class InitializationChecker {
 [. . .]
 protected:
  bool is_initialized_;
};

is_initialized_从InitializationChecker通过其他几个类继承。

InitializationChecker
           ^
           |
MultipleInitializationChecker
  ^
  |
Body
  ^
  |
AcceleratedBody
     ^
     |
SystemBody

Body声明为：

template<typename Type> class Body : public MultipleInitializationChecker {
  using MultipleInitializationChecker::is_initialized_;
 public:
  Body() {
    this->is_initialized_ = false;
  }
  Body(const Scalar<Type> mass__,
       const CartesianVector<Type> position__,
       const CartesianVector<Type> velocity__)
      : mass_(mass__),
        position_(position__),
        velocity_(velocity__) {
          this->is_initialized_ = true;
  }
  [. . .]
  Scalar<Type> mass_;
  CartesianVector<Type> position_;
  CartesianVector<Type> velocity_;
};

我还遇到另一个问题：SystemBody的某些成员无法访问。例如：

error: 'Scalar<double> Body<double>::mass_' is inaccessible

当我尝试执行以下操作时输出

：

SystemBody<double> system_body;
std::cout << system_body.mass_.value();

即使SystemBody只添加了一个不相关的私有成员，AcceleratedBody也是如此声明：

template<typename Type> class AcceleratedBody : public Body<Type> {
  using Body<Type>::is_initialized_;
  using Body<Type>::mass_;
  using Body<Type>::position_;
  using Body<Type>::velocity_;
 public:
  AcceleratedBody() : Body<Type>::Body() {}
  AcceleratedBody(const Scalar<Type> mass__,
                  const CartesianVector<Type> position__,
                  const CartesianVector<Type> velocity__,
                  const CartesianVector<Type> acceleration__)
      : Body<Type>::Body(mass__, position__, velocity__),
        acceleration_(acceleration__) {}
  [. . .]
  CartesianVector<Type> acceleration_;
};

请注意，mass_，position_和velocity_都已在Body公开宣布。

Answer 1

using MultipleInitializationChecker::is_initialized_;在类的私有区域中执行此操作会使其成为私有区域。你甚至不需要那条线。你觉得它做什么？