自己做TypeList编写的测试Demo

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本文介绍了一个使用C++模板元编程实现的TypeListDemo，演示了如何处理类型列表的各种操作，如获取长度、索引查找、追加和删除等。通过一系列的测试验证了这些元编程技巧的有效性和正确性。

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自己编写的TypeListDemo，不错很好玩的东西

#include <iostream>
#include <cassert>
#include <cstring>
using namespace std;

struct NullType {};

template<class Head, class Tail>
struct TypeList
{
	typedef Head HeadType;
	typedef Tail TailType;
};

//仅仅声明，不实现
 template<class TList>
 struct Length;
 
 template<>
 struct Length<NullType>
 {
 	static enum {value = 0,};
 };
 
 template<class Head, class Tail >
 struct Length<TypeList<Head, Tail> >
 {
 	static enum { value = 1 + Length<Tail>::value, };
 };

 template<class, unsigned int> struct TypeAt;
 template<class T, class U>
 struct TypeAt<TypeList<T, U> , 0>
 {
	 typedef T ResultType;
 };

 template<unsigned int index>
 struct TypeAt<NullType, index>
 {
	 typedef NullType ResultType;
 };

 template<class T, class U, unsigned int index>
 struct TypeAt<TypeList<T, U>, index>
 {
	 typedef typename TypeAt<U, index -1>::ResultType ResultType;
 };

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

 template<class Head, class Tail>
 struct IndexOf<TypeList<Head, Tail>, Head>
 {
	 static enum{value = 0,};
 };

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

 template<class Head, class Tail, class T>
 struct IndexOf<TypeList<Head, Tail>, T>
 {
	 static enum {tmpvalue = IndexOf<Tail, T>::value ,};
	 static enum {value = (tmpvalue== -1) ? -1:(tmpvalue+1),};
 };

 template<class, class> struct Append;
 template<class Head, class Tail>
 struct Append<TypeList<Head, Tail>, NullType>
 {
	 typedef NullType ResultType;
 };

 template<class T>
 struct Append<NullType, T>
 {
	 typedef TypeList<T, NullType> ResultType;
 };

 template<class Head, class Tail, class T>
 struct Append<TypeList<Head, Tail>, T>
 {
	 typedef TypeList<Head, typename Append<Tail, T>::ResultType> ResultType;
 };

 template<class, class> struct Erase;
 template<class Head, class Tail>
 struct Erase<TypeList<Head, Tail>, NullType>
 {
	 typedef TypeList<Head, Tail> ResultType;
 };

 template<class T>
 struct Erase<NullType, T>
 {
	 typedef NullType ResultType;
 };

 template<class Head, class Tail>
 struct Erase<TypeList<Head, Tail>, Head>
 {
	 typedef Tail ResultType;
 };

 template<class Head, class Tail, class T>
 struct Erase<TypeList<Head, Tail>, T>
 {
	 typedef typename Erase<Tail, T>::ResultType ResultType;
 };

 template<class T, class U>
 struct IsSame
 {
	 static enum {value = false,};
 };

 template<class T>
 struct IsSame<T, T>
 {
	 static enum {value = true,};
 };

void length_test()
{
	typedef TypeList<int, TypeList<double, TypeList<char, NullType>>> ThreeTypeList;
	assert(Length<ThreeTypeList>::value == 3);

	typedef  TypeAt<ThreeTypeList, 0>::ResultType IntType;
	typedef  TypeAt<ThreeTypeList, 1>::ResultType DoubleType;
	
	int s1 = IsSame<TypeAt<ThreeTypeList, 10000>::ResultType , NullType>::value;

	bool b1 = std::is_same<int, IntType>::value ;
	bool b2 = std::is_same<double, DoubleType>::value;

	assert((IndexOf<ThreeTypeList, int>::value == 0));
	assert((IndexOf<ThreeTypeList,double>::value == 1));
	assert((IndexOf<ThreeTypeList, char>::value == 2));
	assert((IndexOf<ThreeTypeList, NullType>::value == -1));
	assert((IndexOf<ThreeTypeList, std::string>::value == -1));

	typedef Append<ThreeTypeList, double>::ResultType FourTypeList;
	int len = Length<FourTypeList>::value;
	int v1 = IsSame<TypeAt<FourTypeList, 0>::ResultType, int>::value;
	int v2 = IsSame<TypeAt<FourTypeList, 1>::ResultType, double>::value;
	int v3 = IsSame<TypeAt<FourTypeList, 2>::ResultType, char>::value;
	int v4 = IsSame<TypeAt<FourTypeList, 3>::ResultType, double>::value;

	typedef Erase<FourTypeList, int>::ResultType DCDType;
	int e1 = IsSame<TypeAt<DCDType, 0>::ResultType, double>::value;
	int e2 = IsSame<TypeAt<DCDType, 1>::ResultType, char>::value;
	int e3 = IsSame<TypeAt<DCDType, 2>::ResultType, double>::value;

	std::cout<<typeid(DoubleType).name()<<std::endl;

	int aaa = 0;
}

int _tmain(int argc, _TCHAR* argv[])
{
	length_test();

	char c = getchar();
	return 0;
}