最近在看《C++ Template Metaprogramming》，学习模板也知道一些所谓的frist class 编程活动的原理。
元程序-Metaprogram，就是“a program about program”,就是操作代码的程序，我们最熟悉的也就是我们手头使用的编译器了，它将我们写的高级语言的源代码翻译成机器码。
数值计算是元编程应用的一个方面，它将运行期的计算提前到编译期，从而获得运行更快的程序。还有一个应用是在类型计算。
元函数和元数据是元编程的操作对象。
元函数的定义：
一个类模板，它的所有参数都是类型，或者是一个类，带有一个名为“type”的可公共访问的嵌套结构类型。
元数据则复杂的多，两种最常见的是类型和整型，一些类型是为了达到一些效果而使用的外覆类和traits。
下面是我写的一个习题：
对type进行伪英语描述
#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