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;
}