C++-高效的swap

原始版本：

template<typename T>
void swap(T& a, T& b)
{
    T tmp(a);
    a = b;
    b = tmp;
}

此版本不重视效率，当交换的两个对象比较大时，需要更高效的交换，因此应该提供1）public swap成员函数，让它高效的置换两个对象，并提供nono-member swap,调用之

///////////////////////////////////////////////////////////////////////////////
//
//  FileName    :   swap_item25.h
//  Version     :   0.10
//  Author      :   Ryan Han
//  Date        :   2013/07/26 13:13:55
//                    2013/10/30 08:27:50
//  Comment     :
//    ½«WidgetÉùÃ÷Ò»¸öswapµÄpublicº¯Êý×öÕæÕýµÄÖû»¹¤×÷£¬È»ºó½«std::swapÌØ»¯
///////////////////////////////////////////////////////////////////////////////

#ifndef _SWAP_ITEM25_H_
#define _SWAP_ITEM25_H_

#include <iostream>
using namespace std;

class WidgetImpl {
    public:
        WidgetImpl(int a = , int b = , int c = );
        /*WidgetImpl(int a = 1, int b = 2, int c = 3) : x(a), y(b), z(c){
            cout << "WidgetImpl constructor called." << endl;
        }*/

        ~WidgetImpl(){
            cout << "WidgetImpl de-constructor called." << endl;
        }

        void WidgetPrint(){
            cout << "x = " << x << " y = " << y << " z = "<< z << endl;
        }
    private:
        int x, y, z;
};

class Widget {
    public:
        Widget(int a = , int b = , int c = ) : pImpl(new WidgetImpl(a, b, c)){
            cout << "Widget constructor called." << endl;
            ;
        }

        ~Widget(){
            cout << "Widget de-constructor called." << endl;
            delete pImpl;
        }

        Widget(const Widget& rhs) {
            pImpl = new WidgetImpl(*(rhs.pImpl));
        }

        Widget& operator=(const Widget& rhs){
            *pImpl = *(rhs.pImpl);
        }

        void WidgetPrint(){
            pImpl->WidgetPrint();
            //non friend class can't access private data
            //cout << (*pImpl).x << endl;
        }

        //has to use because only member function could access private member pImpl
        void swap(Widget& other){
            using std::swap;
            swap(pImpl, other.pImpl);
        }
    private:
        WidgetImpl* pImpl;
};

//inline to avoid duplicate definition
//http://www.cnblogs.com/dracohan/p/3401660.html
namespace std {
    template <>
    inline void swap<Widget>(Widget& a, Widget& b){
        cout << "specialized swap was called" << endl;
        a.swap(b);
    }
}

#endif

///////////////////////////////////////////////////////////////////////////////
//
//  FileName    :   swap_item25.cpp
//  Version     :   0.10
//  Author      :   Ryan Han
//  Date        :   2013/07/26 13:13:55
//                    2013/10/30 08:27:50
//  Comment     :
//
///////////////////////////////////////////////////////////////////////////////

#include "swap_item25.h"
#include <iostream>
using namespace std;

WidgetImpl::
WidgetImpl(int a, int b, int c) : x(a), y(b), z(c){
            cout << "WidgetImpl constructor called." << endl;
        }

///////////////////////////////////////////////////////////////////////////////
//
//  FileName    :   swap_item25.cpp
//  Version     :   0.10
//  Author      :   Ryan Han
//  Date        :   2013/07/26 13:13:55
//                    2013/10/30 08:27:50
//  Comment     :
//
///////////////////////////////////////////////////////////////////////////////

#include "swap_item25.h"
#include <iostream>
using namespace std;

int main()
{
    Widget a;
    Widget b(,,);

    a.WidgetPrint();
    b.WidgetPrint();

    swap(a, b);

    a.WidgetPrint();
    b.WidgetPrint();

    int* pinta = new int();
    int* pintb = pinta;

    cout << "*pinta is: " << *pinta << endl;
    cout << "*pintb is: " << *pintb << endl;

    return ;
}