C++ 使用另一个助推融合序列创建新的助推融合序列
给定一个融合序列X,我想创建一个新的融合序列Y,其实现将基于X。特别是,我想创建一个类模板C++ 使用另一个助推融合序列创建新的助推融合序列,c++,template-meta-programming,boost-fusion,C++,Template Meta Programming,Boost Fusion,给定一个融合序列X,我想创建一个新的融合序列Y,其实现将基于X。特别是,我想创建一个类模板make_fusion_compliance,以便 template <class X> struct another_fusion_sequence : make_fusion_conforming <X> {}; 不幸的是,尝试使用begin迭代器失败 #include <boost/fusion/include/vector.hpp> template <
make_fusion_compliance
,以便
template <class X>
struct another_fusion_sequence : make_fusion_conforming <X> {};
不幸的是,尝试使用begin迭代器失败
#include <boost/fusion/include/vector.hpp>
template <class... T>
struct sequence1
: make_fusion_conforming< fusion::vector<T...>, sequence1<T...> > {
};
using seq1 = sequence1<int, float, double>;
// the below fails with:
// No type named 'type' in 'boost::fusion::result_of::begin<sequence1<int, float, double> >'
using test1 = fusion::result_of::begin<seq1>::type;
int main() {}
#包括
模板
结构序列1
:使融合一致{
};
使用seq1=sequence1;
//以下操作失败:
//“boost::fusion::result\u of::begin”中没有名为“type”的类型
使用test1=fusion::result\u of::begin::type;
int main(){}
有人能帮我吗?谢谢你问题似乎在于这一推进。Fusion的扩展机制没有认识到使Fusion一致是一个“序列外观”。fusion在处理内部操作(开始、结束、值_at等)时做的第一件事是检查相关序列的标记。它首先检查您的类型是否有
fusion\u标记
关联类型(并将其作为其标记),然后检查它是否是MPL序列,如果检查失败,则确定该序列有非fusion\u标记
标记。为了让所有样板文件都能工作,sequence1
的标签需要是sequence\u facade\u标签
,您可以通过从sequence\u facade
派生,也可以从Base
派生(fusion::vector
在这种情况下,它的标签是vector\u标签
)您已使fusion\u标记
不明确,因此tag\u of::type
变为非fusion\u标记
。一个可能的解决方案是使用fusion_tag=fusion::sequence_facade_tag添加代码>到使融合一致
解决歧义(另一个可能是专门化boost::fusion::traits::tag of::type
)
问题似乎在于这种推进。Fusion的扩展机制没有认识到,使Fusion一致性是一种“序列外观”。fusion在处理内部操作(开始、结束、值_at等)时做的第一件事是检查相关序列的标记。它首先检查您的类型是否有fusion\u标记
关联类型(并将其作为其标记),然后检查它是否是MPL序列,如果检查失败,则确定该序列有非fusion\u标记
标记。为了让所有样板文件都能工作,sequence1
的标签需要是sequence\u facade\u标签
,您可以通过从sequence\u facade
派生,也可以从Base
派生(fusion::vector
在这种情况下,它的标签是vector\u标签
)您已使fusion\u标记
不明确,因此tag\u of::type
变为非fusion\u标记
。一个可能的解决方案是使用fusion_tag=fusion::sequence_facade_tag添加代码>到使融合一致
解决歧义(另一个可能是专门化boost::fusion::traits::tag of::type
)
#include <boost/fusion/iterator/iterator_facade.hpp>
#include <boost/fusion/iterator/value_of.hpp>
#include <boost/fusion/iterator/deref.hpp>
#include <boost/fusion/iterator/next.hpp>
#include <boost/fusion/iterator/prior.hpp>
#include <boost/fusion/iterator/distance.hpp>
#include <boost/fusion/include/begin.hpp>
#include <boost/fusion/include/end.hpp>
#include <boost/fusion/include/size.hpp>
#include <boost/fusion/include/category_of.hpp>
#include <boost/fusion/sequence/sequence_facade.hpp>
namespace fusion = boost::fusion;
// Sequence is the sequence I want to make fusion-conforming
// BaseIter is a fusion-conforming iterator
// the implementation of iterator below is based entirely on BaseIter
template <class Sequence, class BaseIter>
struct iterator
: fusion::iterator_facade<iterator<Sequence, BaseIter>, typename fusion::traits::category_of<BaseIter>::type> {
using base_iter_type = BaseIter;
BaseIter m_base_iter;
iterator(BaseIter base_iter)
: m_base_iter(base_iter){}
template <class It>
struct value_of {
using type = typename fusion::result_of::value_of<typename It::base_iter_type>::type;
};
template <class It>
struct deref {
using type = typename fusion::result_of::deref<typename It::base_iter_type>::type;
static type call(const It& iter) {
return fusion::deref(iter.m_base_iter);
}
};
template <class It>
struct next {
using type = typename fusion::result_of::next<typename It::base_iter_type>::type;
static type call(const It& iter) {
return fusion::next(iter.m_base_iter);
}
};
template <class It>
struct prior {
using type = typename fusion::result_of::prior<typename It::base_iter_type>::type;
static type call(const It& iter) {
return fusion::prior(iter.m_base_iter);
}
};
template <class It1, class It2>
struct distance {
using type = typename fusion::result_of::distance<typename It1::base_iter_type, typename It2::base_iter_type>::type;
static type call(const It1& iter1, const It2& iter2) {
return fusion::distance(iter1.m_base_iter, iter2.m_base_iter);
}
};
};
// Base is the fusion-conforming sequence
// Sequence is the sequence I want to make fusion-conforming
// once again, implementation is based entirely on the Base sequence
template <class Base, class Sequence>
struct make_fusion_conforming
: public Base
, public fusion::sequence_facade<Sequence, typename fusion::traits::category_of<Base>::type> {
using Base::Base;
template <class Seq>
struct begin {
using type = iterator<Seq, typename fusion::result_of::begin<Base>::type>;
static type call(Seq& seq) {
return type(fusion::begin(static_cast<Base&>(seq)));
}
};
template <class Seq>
struct end {
using type = iterator<Seq, typename fusion::result_of::end<Base>::type>;
static type call(Seq& seq) {
return type(fusion::end(static_cast<Base&>(seq)));
}
};
template <class Seq>
struct size {
using type = typename fusion::result_of::size<Base>::type;
static type call(Seq& seq) {
return fusion::size(static_cast<Base&>(seq));
}
};
template <class Seq>
struct empty {
using type = typename fusion::result_of::empty<Base>::type;
static type call(Seq& seq) {
return fusion::empty(static_cast<Base&>(seq));
}
};
template <class Seq, class N>
struct at {
using type = typename fusion::result_of::at<Base, N>::type;
static type call(Seq& seq) {
return fusion::at<N>(static_cast<Base&>(seq));
}
};
template <class Seq, class N>
struct value_at {
using type = typename fusion::result_of::value_at<Base, N>::type;
};
};
#include <boost/fusion/include/vector.hpp>
template <class... T>
struct sequence1
: make_fusion_conforming< fusion::vector<T...>, sequence1<T...> > {
};
using seq1 = sequence1<int, float, double>;
// the below fails with:
// No type named 'type' in 'boost::fusion::result_of::begin<sequence1<int, float, double> >'
using test1 = fusion::result_of::begin<seq1>::type;
int main() {}