C++: TypeList

最新推荐文章于 2024-06-24 22:20:07 发布

转载最新推荐文章于 2024-06-24 22:20:07 发布 · 180 阅读

文章标签：

#c/c++

本文介绍了一个使用C++模板元编程实现的基本类型列表处理系统。该系统包括类型列表的定义、获取列表长度、按索引获取类型、查找类型的索引以及列表的追加操作。通过具体的代码示例展示了如何定义类型列表并进行各种操作。

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#include <stdio.h>
#include <typeinfo.h>
//
// TypeList
//
template <class T, class U>
struct TypeList
{
   typedef T Head;
   typedef U Tail;
};

struct NullType
{
};

#define TYPELIST_1(T1)           TypeList<T1, NullType>
#define TYPELIST_2(T1, T2)       TypeList<T1, TYPELIST_1(T2) >
#define TYPELIST_3(T1, T2, T3)   TypeList<T1, TYPELIST_2(T2,T3) >

//
// Length
//
template <class TList> struct Length;

template <> struct Length<NullType >
{
   enum {value = 0};
};

template <class T,class U>
struct Length<TypeList<T,U> >
{
   enum {value = 1 + Length<U>::value};
};

//
// TypeAt
//
template <class TList, unsigned int index> struct TypeAt;

template <class Head, class Tail> struct TypeAt< TypeList<Head,Tail>,0 >
{
   typedef Head Result;
};

template <class Head, class Tail, unsigned int index> struct TypeAt< TypeList<Head,Tail>,index >
{
   typedef typename TypeAt<Tail, index-1>::Result Result;
};

//
// IndexOf
//
template <class TList, class T> struct IndexOf;

template <class T> struct IndexOf< NullType, T >
{
   enum {value = -1};
};
template <class T,class Tail> struct IndexOf< TypeList<T, Tail>, T >
{
   enum {value = 0};
};

template <class Head,class Tail, class T> struct IndexOf< TypeList<Head, Tail>, T >
{
private:
   enum { temp = IndexOf<Tail,T>::value };
public:
   enum { value = temp==-1 ? -1 : 1 + temp};
};

//
// Append
//
template <class TList, class T> struct Append;

//
// push_front
//
template <class TList, class T> struct push_front
{
   typedef TypeList<T, >
};

int main(int argc, char *argv[])
{
   printf("Hello, world\n");

   typedef TYPELIST_3(int, float,char) MyTypeList;
   printf("MyTypeList length %d\n", Length<MyTypeList>::value);

   printf("MyTypeList TypeAt 0 %s\n", typeid(TypeAt<MyTypeList,0>::Result).name());
   printf("MyTypeList IndexOf<int> %d\n", IndexOf<MyTypeList, float>::value);

   return 0;
}