以下代码的目的是显示结构的内容。它基于this答案。
#include <iostream>
#include <boost/fusion/adapted/struct/adapt_struct.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/for_each.hpp>
#include <boost/mpl/for_each.hpp>
#include <boost/mpl/range_c.hpp>
#include <boost/bind.hpp>
struct Node {
int a = 4;
double b = 2.2;
};
BOOST_FUSION_ADAPT_STRUCT(Node, b)
struct print_visitor {
template <class Index, class C> void operator()(Index, C &c) {
std::cout << boost::fusion::extension::struct_member_name<
C, Index::value>::call() << "="
<< boost::fusion::at<Index>(c) << std::endl;
}
};
template <class C> void print_fields(C &c) {
typedef boost::mpl::range_c<
int, 0, boost::fusion::result_of::size<C>::type::value> range;
boost::mpl::for_each<range>(
boost::bind<void>(print_visitor(), _1, boost::ref(c)));
}
int main() {
Node n;
print_fields(n);
}
编译器（gcc版本4.8.2）抱怨：
无效使用不完整类型'struct boost :: fusion :: result_of :: at＆lt; Node，mpl _ :: integral_c＆lt; int，0＆gt; ＆GT;” typedef typename T :: type type;
原因是什么？如何解决？
以下是编译器的完整输出：
-*- mode: compilation; default-directory: "~/SearchLib/AstarWithPolicies/temp/" -*-
Compilation started at Thu Dec 10 11:54:27
make -k
g++ -Wall -Wextra -Werror -std=c++11 -pedantic -I ~/boost_1_59_0 -I /usr/include/cairomm-1.0/ -I /usr/include/cairo/ -I /usr/include/sigc++-2.0/ -I /usr/lib/x86_64-linux-gnu/sigc++-2.0/include/ -I /usr/include/freetype2/ -g -c temp.cpp
In file included from /home/meir/boost_1_59_0/boost/utility/enable_if.hpp:15:0,
from /home/meir/boost_1_59_0/boost/fusion/support/tag_of.hpp:11,
from /home/meir/boost_1_59_0/boost/fusion/support/category_of.hpp:12,
from /home/meir/boost_1_59_0/boost/fusion/adapted/struct/detail/extension.hpp:14,
from /home/meir/boost_1_59_0/boost/fusion/adapted/struct/adapt_struct.hpp:27,
from temp.cpp:7:
/home/meir/boost_1_59_0/boost/core/enable_if.hpp: In instantiation of ‘struct boost::lazy_disable_if_c<false, boost::fusion::result_of::at<Node, mpl_::integral_c<int, 0> > >’:
/home/meir/boost_1_59_0/boost/core/enable_if.hpp:70:10: required from ‘struct boost::lazy_disable_if<boost::is_const<Node>, boost::fusion::result_of::at<Node, mpl_::integral_c<int, 0> > >’
/home/meir/boost_1_59_0/boost/fusion/sequence/intrinsic_fwd.hpp:102:5: required by substitution of ‘template<class N, class Sequence> constexpr typename boost::lazy_disable_if<boost::is_const<Sequence>, boost::fusion::result_of::at<Sequence, N> >::type boost::fusion::at(Sequence&) [with N = mpl_::integral_c<int, 0>; Sequence = Node]’
temp.cpp:26:48: required from ‘void print_visitor::operator()(Index, C&) [with Index = mpl_::integral_c<int, 0>; C = Node]’
/home/meir/boost_1_59_0/boost/bind/bind.hpp:315:34: required from ‘void boost::_bi::list2<A1, A2>::operator()(boost::_bi::type<void>, F&, A&, int) [with F = print_visitor; A = boost::_bi::list1<mpl_::integral_c<int, 0>&>; A1 = boost::arg<1>; A2 = boost::reference_wrapper<Node>]’
/home/meir/boost_1_59_0/boost/bind/bind.hpp:907:50: required from ‘boost::_bi::bind_t<R, F, L>::result_type boost::_bi::bind_t<R, F, L>::operator()(A1&&) [with A1 = mpl_::integral_c<int, 0>&; R = void; F = print_visitor; L = boost::_bi::list2<boost::arg<1>, boost::reference_wrapper<Node> >; boost::_bi::bind_t<R, F, L>::result_type = void]’
/home/meir/boost_1_59_0/boost/mpl/for_each.hpp:78:25: required from ‘static void boost::mpl::aux::for_each_impl<false>::execute(Iterator*, LastIterator*, TransformFunc*, F) [with Iterator = boost::mpl::r_iter<mpl_::integral_c<int, 0> >; LastIterator = boost::mpl::r_iter<mpl_::integral_c<int, 1> >; TransformFunc = boost::mpl::identity<mpl_::na>; F = boost::_bi::bind_t<void, print_visitor, boost::_bi::list2<boost::arg<1>, boost::reference_wrapper<Node> > >]’
/home/meir/boost_1_59_0/boost/mpl/for_each.hpp:105:97: required from ‘void boost::mpl::for_each(F, Sequence*, TransformOp*) [with Sequence = boost::mpl::range_c<int, 0, 1>; TransformOp = boost::mpl::identity<mpl_::na>; F = boost::_bi::bind_t<void, print_visitor, boost::_bi::list2<boost::arg<1>, boost::reference_wrapper<Node> > >]’
/home/meir/boost_1_59_0/boost/mpl/for_each.hpp:118:48: required from ‘void boost::mpl::for_each(F, Sequence*) [with Sequence = boost::mpl::range_c<int, 0, 1>; F = boost::_bi::bind_t<void, print_visitor, boost::_bi::list2<boost::arg<1>, boost::reference_wrapper<Node> > >]’
temp.cpp:34:62: required from ‘void print_fields(C&) [with C = Node]’
temp.cpp:39:19: required from here
/home/meir/boost_1_59_0/boost/core/enable_if.hpp:63:30: error: invalid use of incomplete type ‘struct boost::fusion::result_of::at<Node, mpl_::integral_c<int, 0> >’
typedef typename T::type type;
^
In file included from /home/meir/boost_1_59_0/boost/fusion/sequence/intrinsic/begin.hpp:14:0,
from /home/meir/boost_1_59_0/boost/fusion/algorithm/iteration/detail/for_each.hpp:11,
from /home/meir/boost_1_59_0/boost/fusion/algorithm/iteration/for_each.hpp:12,
from /home/meir/boost_1_59_0/boost/fusion/include/for_each.hpp:11,
from temp.cpp:9:
/home/meir/boost_1_59_0/boost/fusion/sequence/intrinsic_fwd.hpp:53:16: error: declaration of ‘struct boost::fusion::result_of::at<Node, mpl_::integral_c<int, 0> >’
struct at;
^
temp.cpp: In instantiation of ‘void print_visitor::operator()(Index, C&) [with Index = mpl_::integral_c<int, 0>; C = Node]’:
/home/meir/boost_1_59_0/boost/bind/bind.hpp:315:34: required from ‘void boost::_bi::list2<A1, A2>::operator()(boost::_bi::type<void>, F&, A&, int) [with F = print_visitor; A = boost::_bi::list1<mpl_::integral_c<int, 0>&>; A1 = boost::arg<1>; A2 = boost::reference_wrapper<Node>]’
/home/meir/boost_1_59_0/boost/bind/bind.hpp:907:50: required from ‘boost::_bi::bind_t<R, F, L>::result_type boost::_bi::bind_t<R, F, L>::operator()(A1&&) [with A1 = mpl_::integral_c<int, 0>&; R = void; F = print_visitor; L = boost::_bi::list2<boost::arg<1>, boost::reference_wrapper<Node> >; boost::_bi::bind_t<R, F, L>::result_type = void]’
/home/meir/boost_1_59_0/boost/mpl/for_each.hpp:78:25: required from ‘static void boost::mpl::aux::for_each_impl<false>::execute(Iterator*, LastIterator*, TransformFunc*, F) [with Iterator = boost::mpl::r_iter<mpl_::integral_c<int, 0> >; LastIterator = boost::mpl::r_iter<mpl_::integral_c<int, 1> >; TransformFunc = boost::mpl::identity<mpl_::na>; F = boost::_bi::bind_t<void, print_visitor, boost::_bi::list2<boost::arg<1>, boost::reference_wrapper<Node> > >]’
/home/meir/boost_1_59_0/boost/mpl/for_each.hpp:105:97: required from ‘void boost::mpl::for_each(F, Sequence*, TransformOp*) [with Sequence = boost::mpl::range_c<int, 0, 1>; TransformOp = boost::mpl::identity<mpl_::na>; F = boost::_bi::bind_t<void, print_visitor, boost::_bi::list2<boost::arg<1>, boost::reference_wrapper<Node> > >]’
/home/meir/boost_1_59_0/boost/mpl/for_each.hpp:118:48: required from ‘void boost::mpl::for_each(F, Sequence*) [with Sequence = boost::mpl::range_c<int, 0, 1>; F = boost::_bi::bind_t<void, print_visitor, boost::_bi::list2<boost::arg<1>, boost::reference_wrapper<Node> > >]’
temp.cpp:34:62: required from ‘void print_fields(C&) [with C = Node]’
temp.cpp:39:19: required from here
temp.cpp:26:48: error: no matching function for call to ‘at(Node&)’
<< boost::fusion::at<Index>(c) << std::endl;
^
temp.cpp:26:48: note: candidates are:
In file included from /home/meir/boost_1_59_0/boost/fusion/sequence/intrinsic/begin.hpp:14:0,
from /home/meir/boost_1_59_0/boost/fusion/algorithm/iteration/detail/for_each.hpp:11,
from /home/meir/boost_1_59_0/boost/fusion/algorithm/iteration/for_each.hpp:12,
from /home/meir/boost_1_59_0/boost/fusion/include/for_each.hpp:11,
from temp.cpp:9:
/home/meir/boost_1_59_0/boost/fusion/sequence/intrinsic_fwd.hpp:102:5: note: template<class N, class Sequence> constexpr typename boost::lazy_disable_if<boost::is_const<Sequence>, boost::fusion::result_of::at<Sequence, N> >::type boost::fusion::at(Sequence&)
at(Sequence& seq);
^
/home/meir/boost_1_59_0/boost/fusion/sequence/intrinsic_fwd.hpp:102:5: note: substitution of deduced template arguments resulted in errors seen above
/home/meir/boost_1_59_0/boost/fusion/sequence/intrinsic_fwd.hpp:107:5: note: template<class N, class Sequence> constexpr typename boost::fusion::result_of::at<const Sequence, N>::type boost::fusion::at(const Sequence&)
at(Sequence const& seq);
^
/home/meir/boost_1_59_0/boost/fusion/sequence/intrinsic_fwd.hpp:107:5: note: template argument deduction/substitution failed:
/home/meir/boost_1_59_0/boost/fusion/sequence/intrinsic_fwd.hpp: In substitution of ‘template<class N, class Sequence> constexpr typename boost::fusion::result_of::at<const Sequence, N>::type boost::fusion::at(const Sequence&) [with N = mpl_::integral_c<int, 0>; Sequence = Node]’:
temp.cpp:26:48: required from ‘void print_visitor::operator()(Index, C&) [with Index = mpl_::integral_c<int, 0>; C = Node]’
/home/meir/boost_1_59_0/boost/bind/bind.hpp:315:34: required from ‘void boost::_bi::list2<A1, A2>::operator()(boost::_bi::type<void>, F&, A&, int) [with F = print_visitor; A = boost::_bi::list1<mpl_::integral_c<int, 0>&>; A1 = boost::arg<1>; A2 = boost::reference_wrapper<Node>]’
/home/meir/boost_1_59_0/boost/bind/bind.hpp:907:50: required from ‘boost::_bi::bind_t<R, F, L>::result_type boost::_bi::bind_t<R, F, L>::operator()(A1&&) [with A1 = mpl_::integral_c<int, 0>&; R = void; F = print_visitor; L = boost::_bi::list2<boost::arg<1>, boost::reference_wrapper<Node> >; boost::_bi::bind_t<R, F, L>::result_type = void]’
/home/meir/boost_1_59_0/boost/mpl/for_each.hpp:78:25: required from ‘static void boost::mpl::aux::for_each_impl<false>::execute(Iterator*, LastIterator*, TransformFunc*, F) [with Iterator = boost::mpl::r_iter<mpl_::integral_c<int, 0> >; LastIterator = boost::mpl::r_iter<mpl_::integral_c<int, 1> >; TransformFunc = boost::mpl::identity<mpl_::na>; F = boost::_bi::bind_t<void, print_visitor, boost::_bi::list2<boost::arg<1>, boost::reference_wrapper<Node> > >]’
/home/meir/boost_1_59_0/boost/mpl/for_each.hpp:105:97: required from ‘void boost::mpl::for_each(F, Sequence*, TransformOp*) [with Sequence = boost::mpl::range_c<int, 0, 1>; TransformOp = boost::mpl::identity<mpl_::na>; F = boost::_bi::bind_t<void, print_visitor, boost::_bi::list2<boost::arg<1>, boost::reference_wrapper<Node> > >]’
/home/meir/boost_1_59_0/boost/mpl/for_each.hpp:118:48: required from ‘void boost::mpl::for_each(F, Sequence*) [with Sequence = boost::mpl::range_c<int, 0, 1>; F = boost::_bi::bind_t<void, print_visitor, boost::_bi::list2<boost::arg<1>, boost::reference_wrapper<Node> > >]’
temp.cpp:34:62: required from ‘void print_fields(C&) [with C = Node]’
temp.cpp:39:19: required from here
/home/meir/boost_1_59_0/boost/fusion/sequence/intrinsic_fwd.hpp:107:5: error: invalid use of incomplete type ‘struct boost::fusion::result_of::at<const Node, mpl_::integral_c<int, 0> >’
/home/meir/boost_1_59_0/boost/fusion/sequence/intrinsic_fwd.hpp:53:16: error: declaration of ‘struct boost::fusion::result_of::at<const Node, mpl_::integral_c<int, 0> >’
struct at;
^
make: *** [all] Error 1
Compilation exited abnormally with code 2 at Thu Dec 10 11:54:27