C ++ Tuple Boost.Range - 获取元素类型的元组？ [英] C++ Tuple of Boost.Range - get Tuple of element types?

问题描述

我正在试验Boost.Range和Boost元组。如果我有一个范围的元组，我如何typedef一个元组或相应的元素值？换句话说，我在 / *？* / 这里代替

I am experimenting with Boost.Range and the Boost Tuple. If I have a Tuple of ranges, how can I typedef a Tuple or the corresponding element values? To put this another way, what do I put in place of /*?*/ here:

typedef boost::tuples::tuple<std::vector<int>&, char[]> TupleOfRanges;
typedef /*?*/ TupleOfElements;

我可以手工做，当然，我会写：

I can do this by hand, of course and I would write:

typedef boost::tuples::tuple<int, char> TupleOfElements;

或甚至：

typedef typename boost::tuples::element<0, TupleOfRanges>::type Range0;
typedef typename boost::tuples::element<1, TupleOfRanges>::type Range1;
typedef typename boost::range_iterator<Range0>::type Iterator0;
typedef typename boost::range_iterator<Range1>::type Iterator1;
typedef typename boost::iterator_value<Iterator0>::type Value0;
typedef typename boost::iterator_value<Iterator1>::type Value1;

typedef boost::tuples::tuple<Value0, Value1> TupleOfElements;

但我认为应该可以派生 TupleOfElements 直接从 TupleOfRanges ，无论元组大小。任何想法欢迎！

But I think it should be possible to derive TupleOfElements directly from TupleOfRanges, whatever the tuple size. Any ideas welcome!

编辑：这似乎工作，感谢@ltjax：

this seems to work, thanks @ltjax:

struct GetIteratorType
{
    template <class Range>
    struct apply
    {
        typedef typename boost::range_iterator<Range>::type type;
    };
};
typedef boost::mpl::transform<TupleOfRanges, GetIteratorType> TupleOfIterators;

struct GetElementType
{
    template <class Iterator>
    struct apply
    {
        typedef typename boost::iterator_value<Iterator>::type type;
    };
};
typedef boost::mpl::transform<TupleOfIterators, GetElementType> TupleOfElements;

推荐答案

使用 boost :: mpl

Use boost::mpl::transform with that typedef chain you wrote as the functor!

请参阅 http://www.boost.org/doc/libs/1_47_0/libs/mpl/doc/refmanual/transform .html

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