STL学习：iterator_traits的代码demo

iterator_traits的demo

泛型编程了解的太少，看到STL的iterator部分，了解了模板、全特化、偏特化受益匪浅，写个demo记录下。

#include
using namespace std;
// define a class
class A{
     
public:
    typedef A value_type;
};
// define a trait
template <class T>
struct my_traits{
     
    typedef typename T::value_type value_type;
};
// specialization
template<class T>
struct my_traits<T *>{
     
    typedef T value_type;
};

// Override Funtion
void print(int){
     
    cout<<"int"<<endl;
}
void print(A){
     
    cout<<"A"<<endl;
}

// template function
template <class T>
void extend_print(T t){
     
    //extect the value type, then make an instance
    print(typename my_traits<T>::value_type());
}
int main(){
     
    int* a = new int(1);
    A b;
    extend_print<A>(b);                //output: A
    extend_print<int*>(a);             //output: int
    // a.type_value b;                 //compile wrong
    // A::type_value() c;              //compile wrong
    return 0;
}