我已经有一段时间没有做这个了,但这是我的第一次尝试。毫无疑问,它可以得到改进。
template<unsigned fixedIndex, class T>
class DynamicTupleGetter
{
typedef typename std::tuple_element<fixedIndex, T>::type RetType;
public:
static RetType get(unsigned dynIndex, const T& tupleInstance)
{
const RetType& ret = std::get<fixedIndex>(tupleInstance);
if (fixedIndex == dynIndex)
return ret;
return DynamicTupleGetter<fixedIndex - 1, T>::get(dynIndex, tupleInstance);
}
};
template<class T>
class DynamicTupleGetter<0, T>
{
typedef typename std::tuple_element<0, T>::type RetType;
public:
static RetType get(unsigned dynIndex, const T& tupleInstance)
{
assert(dynIndex == 0);
return std::get<0>(tupleInstance);
}
};
template<class Source>
struct Converter
{
typedef typename std::tuple_element<0, Source>::type Zeroth;
typedef typename std::tuple_element<1, Source>::type First;
static const size_t size0 = std::tuple_size<Zeroth>::value;
static const size_t size1 = std::tuple_size<First>::value;
static const size_t outerProductSize = size0 * size1;
typedef typename std::tuple_element<0, Zeroth>::type BaseType0;
typedef typename std::tuple_element<0, First>::type BaseType1;
typedef typename std::tuple<BaseType0, BaseType1> EntryType;
typedef std::array<EntryType, outerProductSize> DestinationType;
DestinationType create(const Source& source)
{
Zeroth zeroth = std::get<0>(source);
First first = std::get<1>(source);
typedef typename DynamicTupleGetter<size0 -1, Zeroth> ZerothGetter;
typedef typename DynamicTupleGetter<size1 -1, First> FirstGetter;
DestinationType result;
size_t resultIndex = 0;
for(size_t i = 0; i < size0; ++i)
for(size_t j = 0; j < size1; ++j)
{
std::get<0>(result[resultIndex]) = ZerothGetter::get(i, zeroth) ;
std::get<1>(result[resultIndex]) = FirstGetter::get(j, first);
++resultIndex;
}
return result;
}
};
template<class T>
void create(const T& source)
{
Converter<T> converter;
Converter<T>::DestinationType result = converter.create(source);
std::cout << std::get<0>(std::get<3>(result)) << "," << std::get<1>(std::get<3>(result)) << std::endl;
}
auto intPart = std::make_tuple(2,5,9);
auto stringPart = std::make_tuple("foo","bar");
auto source = std::make_tuple(intPart, stringPart);
void f()
{
create(source);
}
index<size>
类型的size_t
(基本上是size_t
的 n 元组)。创建一个序列模板类型,其中包含值为0
到 #vectors-1。创建一个推断返回元组类型的模板。创建一个递归函数,对返回的笛卡尔积中的每个索引进行循环遍历(传入一个函数来生成给定深度的最大索引)。使用 seq 在vector
的index
和tuple
上进行索引,并将调用包装在()...
中,直接构造结果元素的tuple
。然后就完成了。 - Yakk - Adam Nevraumontget
调用:http://stackoverflow.com/questions/13447063/how-would-i-generate-variadic-parameters/13448540#13448540 以及这里有一堆无法工作的代码,可能包含一些有用的东西:http://ideone.com/reaDYi - Yakk - Adam Nevraumont