1.
namespace __inner
{
template<typename _T> char fun(_T*);
template<typename _T> long fun(...);
}template<typename _Base, typename _Sub>
struct is_same_type
{
enum{value = sizeof(char) == sizeof(__inner::fun<_Base>((_Sub*)0)) };
};
class ISupportInitialize
{
public:
virtual void Initialize() = 0;
};class Foo: public ISupportInitialize
{
public:
virtual void Initialize(){ cout<<"Initialize"<<endl; };
};template<bool>
class dispatcher
{
public:
template<typename _T>
dispatcher(_T& r){}
};template<> class dispatcher<true>
{
public:
template<typename _T>
dispatcher(_T& r)
{
r.Initialize();
}
};template<class T> void function( T t )
{
(dispatcher<is_same_type<ISupportInitialize, T>::value>(t));
}int main()
{
Foo x;
int y;
function(x);
function(y);
}2.
namespace __inner
{
template<typename _T> char fun(_T*);
template<typename _T> long fun(...);
}template<typename _Base, typename _Sub>
struct is_same_type
{
enum{value = sizeof(char) == sizeof(__inner::fun<_Base>((_Sub*)0)) };
};
class ISupportInitialize
{
public:
virtual void Initialize() = 0;
};class Foo: public ISupportInitialize
{
public:
virtual void Initialize(){ cout<<"Initialize"<<endl; };
};template<bool>
class dispatcher
{
public:
template<typename _T>
dispatcher(_T& r){}
};
template<> class dispatcher<false> //***************就改了这一行*************
{
public:
template<typename _T>
dispatcher(_T& r)
{
r.Initialize();
}
};template<class T> void function( T t )
{
(dispatcher<is_same_type<ISupportInitialize, T>::value>(t));
}int main()
{
Foo x;
int y;
function(x);
function(y);
}以上两份代码, 为什么第一份能编译, 而第二份不能编译(只把"true"改成了"false") !(只要求能编译, 不管逻辑是否正确), 请达人解释
namespace __inner
{
template<typename _T> char fun(_T*);
template<typename _T> long fun(...);
}template<typename _Base, typename _Sub>
struct is_same_type
{
enum{value = sizeof(char) == sizeof(__inner::fun<_Base>((_Sub*)0)) };
};
class ISupportInitialize
{
public:
virtual void Initialize() = 0;
};class Foo: public ISupportInitialize
{
public:
virtual void Initialize(){ cout<<"Initialize"<<endl; };
};template<bool>
class dispatcher
{
public:
template<typename _T>
dispatcher(_T& r){}
};template<> class dispatcher<true>
{
public:
template<typename _T>
dispatcher(_T& r)
{
r.Initialize();
}
};template<class T> void function( T t )
{
(dispatcher<is_same_type<ISupportInitialize, T>::value>(t));
}int main()
{
Foo x;
int y;
function(x);
function(y);
}2.
namespace __inner
{
template<typename _T> char fun(_T*);
template<typename _T> long fun(...);
}template<typename _Base, typename _Sub>
struct is_same_type
{
enum{value = sizeof(char) == sizeof(__inner::fun<_Base>((_Sub*)0)) };
};
class ISupportInitialize
{
public:
virtual void Initialize() = 0;
};class Foo: public ISupportInitialize
{
public:
virtual void Initialize(){ cout<<"Initialize"<<endl; };
};template<bool>
class dispatcher
{
public:
template<typename _T>
dispatcher(_T& r){}
};
template<> class dispatcher<false> //***************就改了这一行*************
{
public:
template<typename _T>
dispatcher(_T& r)
{
r.Initialize();
}
};template<class T> void function( T t )
{
(dispatcher<is_same_type<ISupportInitialize, T>::value>(t));
}int main()
{
Foo x;
int y;
function(x);
function(y);
}以上两份代码, 为什么第一份能编译, 而第二份不能编译(只把"true"改成了"false") !(只要求能编译, 不管逻辑是否正确), 请达人解释
int main()
{
...
function(x); //...
function(y); //...
}
此处,function(x)中,由于x在is_same_type中返回的是true,因此,编译器解释的是偏特化的dispatcher,而x中切好有Initialize,所以没有问题。
如果修改了对应的那行,那么function(y)则会被解释为偏特化的dispatcher,显然,一个int类型是没有Initialize的方法的,故编译失败
#include <iostream>
using namespace std;
namespace __inner
{
template<typename _T> char fun(_T*);
template<typename _T> long fun(...);
}template<typename _Base, typename _Sub>
struct is_same_type
{
enum{value = sizeof(char) == sizeof(__inner::fun<_Base>((_Sub*)0)) };
};
class ISupportInitialize
{
public:
virtual void Initialize() = 0;
};class Foo: public ISupportInitialize
{
public:
virtual void Initialize(){ cout<<"Initialize"<<endl; };
};template<bool>
class dispatcher
{
public:
template<typename _T>
dispatcher(_T& r){}
};template<> class dispatcher<false> //***************就改了这一行*************
{
public:
template<typename _T>
dispatcher(_T& r)
{
r.Initialize();
}
};
template<class T> void function( T t )
{
dispatcher<!is_same_type<ISupportInitialize, T>::value> tempValue(t); //原来的true改为false后,这儿也许也需要改变,因对于int类型 r.Initialize();是编译通不过的。
}
int main()
{
Foo x;
int y=0;
function(x);
function(y);
return 0;
}