C++模板元編程(1)

                     最近在看《C++ Template Metaprogramming》，學習模板也知道一些所謂的frist class 編程活動的原理。

                     元程式-Metaprogram，就是“a program about program”,就是作業碼的程式，我們最熟悉的也就是我們手頭使用的編譯器了，它將我們寫的進階語言的原始碼翻譯成機器碼。

                    數值計算是元編程應用的一個方面，它將運行期的計算提前到編譯期，從而獲得運行更快的程式。還有一個應用是在類型計算。

                    元函數和中繼資料是元編程的操作對象。

                    元函數的定義：

                    一個類模板，它的所有參數都是類型，或者是一個類，帶有一個名為“type”的可公用訪問的嵌套結構類型。

                   

                    中繼資料則複雜的多，兩種最常見的是類型和整型，一些類型是為了達到一些效果而使用的外覆類和traits。

                     下面是我寫的一個習題：   

                      對type進行偽英語描述

                       #ifndef TYPE_DES_H
#define TYPE_DES_H

#include <iostream>
#include <cstring>

const int MAX = 100;

template <typename T>
struct type_des
{
public:
    operator const char* (){
        return _name;
    }
    static const char* _name;
};

template <typename T>
const char* type_des<T>::_name = "undef type";

template <>
const char* type_des<int>::_name = "int";

template <>
const char* type_des<char>::_name = "char";

template <>
const char* type_des<long>::_name = "long";

template <>
const char* type_des<short>::_name = "short";

template <>
const char* type_des<void>::_name = "void";

template <>
const char* type_des<bool>::_name = "bool";

template <>
const char* type_des<float>::_name = "float";

template <>
const char* type_des<double>::_name = "double";

template <typename T>
struct type_des<T*>
{
    operator const char *(){
        static char temp[MAX];
        strcpy(temp,"pointer to ");
        strcat(temp,type_des<T>());
        return temp;
    }
};

template <typename T>
struct type_des<T&>
{
    operator const char *(){
        static char temp[MAX];
        strcpy(temp,"refence to ");
        strcat(temp,type_des<T>());
        return temp;
    }
};

template <typename T>
struct type_des<const T&>
{
    operator const char *(){
        static char temp[MAX];
        strcpy(temp,"const refence to ");
        strcat(temp,type_des<T>());
        return temp;
    }
};
template <typename T>
struct type_des<const T*>
{
    operator const char *(){
        static char temp[MAX];
        strcpy(temp,"const pointer to ");
        strcat(temp,type_des<T>());
        return temp;
    }
};

template <typename T>
struct type_des<T[]>
{
    operator const char *(){
        static char temp[MAX];
        strcpy(temp,"array of  ");
        strcat(temp,type_des<T>());
        return temp;
    }
};

template <typename T>
struct type_des<T (*)()>
{
    operator const char *(){
        static char temp[MAX];
        strcpy(temp,"function returning ");
        strcat(temp,type_des<T>());
        return temp;
    }
};

template <typename T>
struct type_des<T* (*)()>
{
    operator const char *(){
        static char temp[MAX];
        strcpy(temp,"function returning pointer to ");
        strcat(temp,type_des<T>());
        return temp;
    }
};

template <typename T>
struct type_des<T* (*[])()>
{
    operator const char *(){
        static char temp[MAX];
        strcpy(temp,"array of function returning pointer to ");
        strcat(temp,type_des<T>());
        return temp;
    }
};

template <typename R,typename T>
struct type_des<T* (*[])(R)>
{
    operator const char *(){
        static char temp[MAX];
        strcpy(temp,"array of function with ");
        strcat(temp,type_des<R>());
        strcat(temp," returning pointer to ");
        strcat(temp,type_des<T>());
        return temp;
    }
};

template <typename R,typename T>
struct type_des<const T* (*[])(R)>
{
    operator const char *(){
        static char temp[MAX];
        strcpy(temp,"array of function with ");
        strcat(temp,type_des<R>());
        strcat(temp," returning pointer to const ");
        strcat(temp,type_des<T>());
        return temp;
    }
};

template <typename R,typename T>
struct type_des<const T& (*[])(R)>
{
    operator const char *(){
        static char temp[MAX];
        strcpy(temp,"array of function with ");
        strcat(temp,type_des<R>());
        strcat(temp," returning refence to const ");
        strcat(temp,type_des<T>());
        return temp;
    }
};

#endif // TYPE_DES_H