RAII.cpp

#include <fstream>
#include <iostream>
#include <mutex>
using namespace std;

enum class shape_type {
  circle,
  triangle,
  rectangle,
};

class shape {
public:
  shape() { cout << "shape" << endl; }

  virtual void print() { cout << "I am shape" << endl; }

  virtual ~shape() {}
};

class circle : public shape {
public:
  circle() { cout << "circle" << endl; }

  void print() { cout << "I am circle" << endl; }
};

class triangle : public shape {
public:
  triangle() { cout << "triangle" << endl; }

  void print() { cout << "I am triangle" << endl; }
};

class rectangle : public shape {
public:
  rectangle() { cout << "rectangle" << endl; }

  void print() { cout << "I am rectangle" << endl; }
};

// 利用多态 上转 如果返回值为shape,会存在对象切片问题。
shape *create_shape(shape_type type) {
  switch (type) {
  case shape_type::circle:
    return new circle();
  case shape_type::triangle:
    return new triangle();
  case shape_type::rectangle:
    return new rectangle();
  }
}

class shape_wrapper {
public:
  explicit shape_wrapper(shape *ptr = nullptr) : ptr_(ptr) {}

  ~shape_wrapper() { delete ptr_; }

  shape *get() const { return ptr_; }

private:
  shape *ptr_;
};

void foo() {
  shape_wrapper ptr(create_shape(shape_type::circle));
  ptr.get()->print();
}

int main() {

  // 第一种方式
  shape *sp = create_shape(shape_type::circle);
  sp->print();
  delete sp;

  // 第二种方式
  foo();

  return 0;
}