源码仓库
什么是PImpl机制
Pointer to implementation（PImpl ），通过将类的实现细节放在一个单独的类中，从其对象表示中删除它们，通过一个不透明的指针访问它们（cppreference 是这么说的）
通过一个私有的成员指针，将指针所指向的类的内部实现数据进行隐藏
class Demo {
public:
...
private:
DemoImp* imp_;
}
为什么用PImpl 机制
个人拙见
- C++ 不像Java 后端型代码，能有行业定式的列目录名形成规范（controller、Dao等）
- 隐藏实现，降低耦合性和分离接口（隐藏类的具体实现）
- 通过编译期的封装（隐藏实现类的细节）
业界实现
优秀开源代码有实现
PImpl实现
方法一
cook_cuisine.h
#pragma once
#include <unordered_map>
#include <vector>
#include <memory>
// Pointer to impl ementation
class CookImpl;
// 后厨
class Cook {
public:
Cook(int, const std::vector<std::string>&);
~Cook();
std::vector<std::string> getMenu();
uint32_t getChefNum();
private:
CookImpl* impl_;
};
typedef std::shared_ptr<Cook> CookPtr; // 美妙的typedef 懒人工具cook_cuisine.cc
#include "cook_cuisine.h"
class CookImpl {
public:
CookImpl(uint32_t checf_num, const std::vector<std::string>& menu):checf_num_(checf_num), menu_(menu) {}
std::vector<std::string> getMenu();
uint32_t getChefNum();
private:
uint32_t checf_num_;
std::vector<std::string> menu_;
};
std::vector<std::string> CookImpl::getMenu() {
return menu_;
}
uint32_t CookImpl::getChefNum() {
return checf_num_;
}
Cook::Cook(int chef_num, const std::vector<std::string>& menu) {
impl_ = new CookImpl(chef_num, menu);
}
Cook::~Cook() {
delete impl_;
}
std::vector<std::string> Cook::getMenu() {
return impl_->getMenu();
}
uint32_t Cook::getChefNum() {
return impl_->getChefNum();
}方法二
cook_cuisine.h
#pragma once
#include <unordered_map>
#include <vector>
#include <memory>
#include "cook_cuisine_imp.h"
// 后厨
class Cook {
public:
Cook(int, const std::vector<std::string>&);
~Cook();
std::vector<std::string> getMenu();
uint32_t getChefNum();
private:
CookImplPtr impl_;
};
typedef std::shared_ptr<Cook> CookPtr;cook_cuisine.cc
#include "cook_cuisine.h"
Cook::Cook(int chef_num, const std::vector<std::string>& menu) {
impl_.reset(new CookImpl(chef_num, menu));
}
Cook::~Cook() {
}
std::vector<std::string> Cook::getMenu() {
return impl_->getMenu();
}
uint32_t Cook::getChefNum() {
return impl_->getChefNum();
}cook_cuisine_imp.h
#pragma once
#include <vector>
#include <unordered_map>
#include <memory>
class CookImpl {
public:
CookImpl(uint32_t checf_num, const std::vector<std::string>& menu):checf_num_(checf_num), menu_(menu) {}
std::vector<std::string> getMenu();
uint32_t getChefNum();
private:
uint32_t checf_num_;
std::vector<std::string> menu_;
};
typedef std::shared_ptr<CookImpl> CookImplPtr;cook_cusine_imp.cc
#include "cook_cuisine_imp.h"
std::vector<std::string> CookImpl::getMenu() {
return menu_;
}
uint32_t CookImpl::getChefNum() {
return checf_num_;
}main.cc
#include "cook_cuisine.h"
#include <iostream>
using namespace std; // Testing, 平时开发可千万别用这句
int main() {
int checf_num = 10;
const std::vector<std::string> menus = { "Chicken", "Beef", "Noodle", "Milk" };
CookPtr cook(new Cook(checf_num, menus));
auto cook_menu = cook->getMenu();
auto cook_checf_num = cook->getChefNum();
cout << "======================Chinese Cook======================\n";
cout << "============Checf: " << cook_checf_num << " people\n";
cout << "==========Menu\n";
for (size_t i = 0; i < cook_menu.size(); i++) {
cout << "============" << i + 1 << " : " << cook_menu[i] << "\n";
}
return 0;
}
CMakeLists.txt
mkdir build
cd build
cmake ..
PImpl 缺点
空间开销：每个类都需要额外的指针内存指向实现类
时间开销：每个类间接访问实现的时候多一个间接指针操作的开销
阅读开销：使用、阅读和调试上带来一些不便（不是啥问题）
总结
每种设计方法都有它的优点和缺点
PImpl 用一些内存空间和额外类的实现换取耦合性的下降，是可以接受的
但重点在：在性能/内存要求不敏感处，PImpl 技术才更优不错的发挥舞台
极端例子：
你不可能在斐波那契的实现中还加个PImpl 机制，多此一举
到此这篇关于C++ pimpl机制详细讲解的文章就介绍到这了,更多相关C++ pimpl机制内容请搜索编程网以前的文章或继续浏览下面的相关文章希望大家以后多多支持编程网！
