Mixin技术学习笔记

​ Mixin(Mix in)是一种将若干个功能独立的类通过继承方式实现模块复用的C++模板编程技巧，其基本用法是将模板参数作为派生类基类，基本语法为：

template <typename... Mixins>
class MixinClass : public Mixins... {
public:
  MixinClass() : Mixins...() {
  
  }
  // ...
};

​ Mixin是一些列被称为 mixin的类型，这些类型分别实现一个单独功能，且这些功能本身是正交的。当需要使用这些功能时，就可以将不同 mixin组合在一起，像搭积木一样，完成功能复用。

#include <iostream>

template <typename... Mixins>
class Point : public Mixins... {
 public:
  Point(double x, double y) : Mixins()..., x_(x), y_(y) {}
  Point() : Mixins()..., x_(0), y_(0) {}
  ~Point() = default;

  [[nodiscard]] double x() const { return x_; }
  [[nodiscard]] double y() const { return y_; }
  void setX(double x) { x_ = x; }
  void setY(double y) { y_ = y; }

private:
  double x_;
  double y_;
};

class Label {
public:
  Label() : label_("default label") {}
  ~Label() = default;
  void setLabel(const std::string& label) { label_ = label; }
  [[nodiscard]] const std::string& label() const { return label_; }

private:
  std::string label_;
};

class Color {
public:
  Color() : red_(0), green_(0), blue_(0) {}
  ~Color() = default;
  void setColor(double red, double green, double blue) {
    red_ = red;
    green_ = green;
    blue_ = blue;
  }
  [[nodiscard]] const double &red() const { return red_; }
  [[nodiscard]] const double &green() const { return green_; }
  [[nodiscard]] const double &blue() const { return blue_; }

private:
  double red_;
  double green_;
  double blue_;
};

using MyPoint = Point<Label, Color>;

int main() {
  MyPoint p(1, 2);
  p.setLabel("point");
  p.setColor(1, 0, 0);
  std::cout << "x: " << p.x() << std::endl;
  std::cout << "y: " << p.y() << std::endl;
  std::cout << "label: " << p.label() << std::endl;
  std::cout << "red: " << p.red() << std::endl;
  std::cout << "green: " << p.green() << std::endl;
  std::cout << "blue: " << p.blue() << std::endl;
  return 0;
}

​ 输出结果：

x: 1
y: 2
label: point
red: 1
green: 0
blue: 0

参考资料：

• [1] C++编程技巧：Mixin