learn_class/modern_cpp_30/smart_ptr/unique_ptr.cpp - master - githubmirror/CPlusPlusThings

learn_class/modern_cpp_30/smart_ptr/unique_ptr.cpp

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zhangxing

support bazel complie this project and format code.

30 мар 2024, 17:00

30 мар 2024, 17:003c8a3f2

//
// Created by light on 19-12-12.
//

#include "../RAII/shape.h"

template <typename T> class unique_ptr {
public:
  explicit unique_ptr(T *ptr = nullptr) noexcept : ptr_(ptr) {}

  ~unique_ptr() noexcept { delete ptr_; }

  T &operator*() const noexcept { return *ptr_; }

  T *operator->() const noexcept { return ptr_; }

  operator bool() const noexcept { return ptr_; }

  T *get() const noexcept { return ptr_; }

  unique_ptr(unique_ptr &&other) noexcept {
    cout << "move ctor" << endl;
    ptr_ = other.release();
  }

  template <typename U> unique_ptr(unique_ptr<U> &&other) noexcept {
    cout << "U move ctor" << endl;
    ptr_ = other.release();
  }

  // copy and swap  始终只有一个对象有管理这块空间的权限
  unique_ptr &operator=(unique_ptr rhs) noexcept {
    rhs.swap(*this);
    return *this;
  }

  // 原来的指针释放所有权
  T *release() noexcept {
    T *ptr = ptr_;
    ptr_ = nullptr;
    return ptr;
  }

  void swap(unique_ptr &rhs) noexcept {
    using std::swap;
    swap(ptr_, rhs.ptr_); // 转移指针所有权
  }

private:
  T *ptr_;
};

template <typename T> void swap(unique_ptr<T> &lhs, unique_ptr<T> &rhs) {
  lhs.swap(rhs);
}

int main() {
  unique_ptr<shape> ptr1{create_shape(shape_type::circle)};
  //    unique_ptr<shape> ptr2{ptr1}; // error
  unique_ptr<shape> ptr2_2{std::move(ptr1)}; // ok
  if (ptr2_2.get() != nullptr && ptr1.get() == nullptr)
    ptr2_2.get()->print();

  unique_ptr<shape> ptr3{create_shape(shape_type::rectangle)};
  //    ptr1 = ptr3;    // error
  ptr3 = std::move(ptr1); // ok
  //    unique_ptr<circle> cl{create_shape(shape_type::circle)};  // error
  //    因为create_shape返回的是shape 不能基类转子类
  unique_ptr<circle> cl{new circle()};
  unique_ptr<shape> ptr5(std::move(cl)); // ok unique<circle>转unique<circle>
}