C++之萃取技术 笔记

#include <iostream>
using namespace std;

//tag
class _xFalse
{};
class _xTrue
{};


template<typename T>
struct traits
{
typedef _xFalse hasDefaultConstructor;
};


class ClsA
{
public:
ClsA(){}
ClsA(const int v) {val = v;}
int val;
};
class ClsB
{
public:
explicit ClsB(int val){this->val = val;}
int val;
};
template<>
struct traits<ClsA>
{
typedef _xTrue hasDefaultConstructor;
};


template<typename T>
class Cls
{
public:
typedef typename traits<T>::hasDefaultConstructor hasDefaultCon;
void fun(T t)
{
_fun(t, hasDefaultCon());
}


private:
void _fun(T t, _xFalse)
{
cout << "fun: xfalse called, has no default constructor" << endl;
}
void _fun(T t, _xTrue)
{
cout << "fun: xTrue called, has default constructor" << endl;
}
};


class TestClass
{


};
void main()
{
ClsA a(10);
ClsB b(10);
Cls<ClsA> clsa;
clsa.fun(a);
Cls<ClsB> clsb;
clsb.fun(b);

}

参考文档：

《type traits 之”本质论”》http://blog.csdn.net/sanlongcai/archive/2007/09/15/1786647.aspx
《traits：Traits技术初探》http://www.cppblog.com/woaidongmao/archive/2008/11/09/66387.html