pimpl示例代码

• 使用pimpl将实现细节移出头文件。

• 将私有成员变量和私有方法移入Impl类，可以实现数据和方法的封装，以避免在公开头文件中声明私有方法。

• 不能在实现类中隐藏虚方法（virtual method），虚方法必须在公开类中出现以便由继承类重载。

• 可以在实现类中加入指向公开类的指针，以便于Impl类调用公开方法。或者也可以将公开类传给需要它的实现类方法。

• 与Bridge Pattern的区别：The Bridge pattern is about object-oriented design, while the PIMPL idiom is about physical design of files.

• 解释：

  But in its basic and common form, a class using PIMPL points to a single implementation, so there is no abstract class with distinct subclasses — just one class, forward declared, and compiled elsewhere. Changing the implementation class does not require any recompilation of sources that include the main header.

  For example, say you have a lot of private member functions, private enums, and private data. And these private "bits" change fairly frequently as the class is developed and maintained. If the #include dependencies are such that touching this header file causes a large number of sources to be recompiled, you have a good candidate for PIMPL.

• 部署pimpl的方法：Making Pimpl Easy

• 相关书籍：Large-Scale C++ Software Design

 

AutoTimer.h

---

#include <boost/shared_ptr.hpp>



class AutoTimer

{



public:

	/// Create a new timer object with a human readable name

	 AutoTimer(const std::string &name);

	/// On destruction, the timer reports how long it was alive

	~AutoTimer();



private:

	// Make this object be noncopyable because it holds a pointer

	AutoTimer(const AutoTimer &);

	const AutoTimer &operator =(const AutoTimer &);

	

	class Impl;

	boost::shared_ptr<Impl> mImpl;



};

 

AutoTimer.cpp

---

#include "StdAfx.h"

#include "AutoTimer.h"

#include <iostream>

#include <windows.h>

#include <string>



class AutoTimer::Impl

{

public:

	double GetElapsed() const

	{

		return (GetTickCount()-mStartTime) / 1e3;

	}

	std::string mName;

	DWORD mStartTime;

};





AutoTimer::AutoTimer(const std::string &name)

: mImpl(new AutoTimer::Impl())

{

	mImpl->mName = name;

	mImpl->mStartTime = GetTickCount();

}



AutoTimer::~AutoTimer(void)

{

 	std::cout<<mImpl->mName<< ": took " << mImpl->GetElapsed()

 		<< " secs" << std::endl;

}

Main.cpp

---

#include "stdafx.h"

#include "AutoTimer.h"

#include <iostream>

using namespace std;



int _tmain(int argc, _TCHAR* argv[])

{

	AutoTimer timer("MyTimer");





	for (int i = 0; i < 10000; ++i)

	{

		cout << ".";

	}

	cout << endl;

	return 0;

}