将任意类型映射到一个唯一整数（C++模板实现TypeList）

From: http://stackoverflow.com/questions/1708458/template-metaprogram-converting-type-to-unique-number

template <class Prev, class This>

class TypeList

{

public:

   enum

   {

      position = (Prev::position) + 1,

   };

};



template <>

class TypeList<void, void>

{

public:

  enum

  {

     position = 0,

  };

};





#include <iostream>



int main()

{

        typedef TypeList< void, void> base;  // base

        typedef TypeList< base, double> t2;  // position is unique id for double

        typedef TypeList< t2, char > t3; // position is unique id for char



        std::cout << "T1 Posn: " << base::position << std::endl;

        std::cout << "T2 Posn: " << t2::position << std::endl;

        std::cout << "T3 Posn: " << t3::position << std::endl;

}

确实是非常巧妙的方法。这个方法在Andrei Alexandrescu的《Modern C++ Design》上有详细说明。

这本书在豆瓣上的评分高达9.0，虽然比不上《The C Programming Language》的9.5，但却比Herb Sutter的《Exceptional C++》的8.5分要高上不少。