typelist的实现
#include <stdio.h>
struct NullType;
template <typename T0 = NullType, typename T1 = NullType, typename T2 =
NullType,
typename T3 = NullType, typename T4 = NullType, typename T5 = NullType>
struct typelist
{
typedef T0 Head;
typedef typelist<T1, T2, T3, T4, T5> Tail;
enum { length = 1 + Tail::length };
};
typename T3 = NullType, typename T4 = NullType, typename T5 = NullType>
struct typelist
{
typedef T0 Head;
typedef typelist<T1, T2, T3, T4, T5> Tail;
enum { length = 1 + Tail::length };
};
template <>
struct typelist<NullType, NullType, NullType, NullType, NullType, NullType>
{
enum { length = 0 };
};
struct typelist<NullType, NullType, NullType, NullType, NullType, NullType>
{
enum { length = 0 };
};
template <typename TL, int n, bool OutOfRange = (n >=
TL::length)>
struct type_at
{
typedef typename type_at<typename TL::Tail, n-1>::type type;
};
struct type_at
{
typedef typename type_at<typename TL::Tail, n-1>::type type;
};
template <typename TL>
struct type_at<TL, 0, false>
{
typedef typename TL::Head type;
};
struct type_at<TL, 0, false>
{
typedef typename TL::Head type;
};
template <typename TL, int n>
struct type_at<TL, n, true>
{
};
struct type_at<TL, n, true>
{
};
template <typename T, typename U>
struct is_same_type
{
enum { value = false };
};
struct is_same_type
{
enum { value = false };
};
template <typename T>
struct is_same_type<T, T>
{
enum { value = true };
};
struct is_same_type<T, T>
{
enum { value = true };
};
template <typename TL, typename T, int count = -1, bool equalsHead
=
is_same_type<typename TL::Head, T>::value>
struct index_of
{
enum { value = 1 + index_of<typename TL::Tail, T, count-1>::value };
};
is_same_type<typename TL::Head, T>::value>
struct index_of
{
enum { value = 1 + index_of<typename TL::Tail, T, count-1>::value };
};
template <typename TL, typename T, int count>
struct index_of<TL, T, count, true>
{
enum { value = 0 };
};
struct index_of<TL, T, count, true>
{
enum { value = 0 };
};
template <typename T, typename U, int count>
struct index_of<typelist<T>, U, count, false>
{
enum { value = count };
};
struct index_of<typelist<T>, U, count, false>
{
enum { value = count };
};
template <typename T, typename U, bool greaterThan = (sizeof(T) >=
sizeof(U))>
struct type_selector
{
typedef T type;
};
struct type_selector
{
typedef T type;
};
template <typename T, typename U>
struct type_selector<T, U, false>
{
typedef U type;
};
struct type_selector<T, U, false>
{
typedef U type;
};
template <typename TL>
struct largest_type
{
typedef typename type_selector<typename TL::Head, typename largest_type<typename
TL::Tail>::type>::type type;
};
struct largest_type
{
typedef typename type_selector<typename TL::Head, typename largest_type<typename
TL::Tail>::type>::type type;
};
template <typename T>
struct largest_type<typelist<T> >
{
typedef T type;
};
struct largest_type<typelist<T> >
{
typedef T type;
};
int main()
{
typedef typelist<int, float, double, char> types;
printf("%d\n", types::length);
type_at<types, 3>::type ch = 'c';
printf("%c\n", ch);
printf("%d\n", index_of<types, unsigned>::value);
printf("%d\n", index_of<types, double>::value);
largest_type<types>::type d = 2.5;
printf("%lf\n", d);
printf("%d\n", index_of<types, largest_type<types>::type>::value);
}
{
typedef typelist<int, float, double, char> types;
printf("%d\n", types::length);
type_at<types, 3>::type ch = 'c';
printf("%c\n", ch);
printf("%d\n", index_of<types, unsigned>::value);
printf("%d\n", index_of<types, double>::value);
largest_type<types>::type d = 2.5;
printf("%lf\n", d);
printf("%d\n", index_of<types, largest_type<types>::type>::value);
}
分类:
C++
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