C++的Traits

1. Think of a trait as a small object whose main purpose is to carry information used by another object or algorithm to determine "policy" or "implementation
details"  ------ Bjarne Stroustrup

2. The
traits class is used in template code to reflect properties (traits) of the actual template argument.

template <typename T>  

struct TraitsHelper {  

     typedef T ret_type;  

     typedef T par_type;  

};  

template <>  

struct TraitsHelper<int> {  

     typedef int ret_type;  

     typedef int par_type;  

};  

template <>  

struct TraitsHelper<float> {  

     typedef float ret_type;  

     typedef int par_type;  

};  

template <typename T>  

class Test {  

public:  

     TraitsHelper<T>::ret_type Compute(TraitsHelper<T>::par_type d);  

private:  

     T mData;  

};