设计模式之pimpl惯用法C++版

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类D使用类A，类B作为成员变量，

以下是头文件

pattern.h

#ifndef PATTERN_H#define PATTERN_Hclass A{public:A(int m);A();void print();private:int m_a;};class B{public:B(int m);B();void print();private:int m_b;};class D{public:D(int a,int b);void print();private:A m_classA;B m_classB;};#endif

pattern.cpp

#include <iostream>#include "pattern.h"A::A(int  m){m_a = m;}A::A(){m_a = 0;}void A::print(){std::cout<<"A "<<m_a<<std::endl;}B::B(int m){m_b = m;}B::B(){m_b =0 ;}void B::print(){std::cout<<"B "<<m_b<<std::endl;}D::D(int a,int b):m_classA(a),m_classB(b){}void D::print(){m_classA.print();m_classB.print();}int main(){D classD(1,2);classD.print();}

A、B与D强耦合。非常不利于后期维护

#ifndef PATTERN2_H#define PATTERN2_Hclass Impl;class D{public:D(int a,int b);void print();~D();private:Impl *m_Impl;};#endif

引入impl指针

pattern2.h

pattern2.cpp

#include <iostream>#include "pattern2.h"class A{public:A(int m);A();void set(int m);void print();private:int m_a;};class B{public:B(int m);B();void set(int m);void print();private:int m_b;};A::A(int  m){m_a = m;}A::A(){m_a = 0;}void A::set(int m){    m_a = m;}void A::print(){std::cout<<"A "<<m_a<<std::endl;}B::B(int m){m_b = m;}B::B(){m_b =0 ;}void B::set(int m){    m_b = m;}class Impl{public:A m_classA;B m_classB;};void B::print(){std::cout<<"B "<<m_b<<std::endl;}D::D(int a,int b):m_Impl(new Impl()){m_Impl->m_classA.set(a);m_Impl->m_classB.set(b);}D::~D(){if(m_Impl){delete m_Impl;m_Impl = NULL;}}void D::print(){m_Impl->m_classA.print();m_Impl->m_classB.print();}int main(){D classD(2,1);classD.print();}

通过Impl *m_Impl;大大降低了A、B与D类的耦合，并且A类和B类的内部的修改不会导致包含D类头文件的其他模块重新编译。

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