使用karma为指针向量生成输出

Question

我在使用karma为boost :: shared_ptrs的向量中保存的结构生成输出时遇到了一些麻烦。我有一个使用不能编译的int的小测试用例。我以为我可以使用deref_iterator自定义点来处理这种情况，或者也许开箱即用的精神会注意到我的容器持有指针类型并进行额外的解引用。无论如何，这是测试用例：

#include <boost/spirit/include/karma.hpp>
#include <boost/shared_ptr.hpp>
#include <vector>

typedef boost::shared_ptr< int > ptr;
typedef std::vector< ptr > vec;

namespace boost {
namespace spirit {
namespace traits {

// specialise how iterators into containers of pointers are dereferenced
template <>
struct deref_iterator< typename container_iterator< vec const >::type >
{
    typedef int type;

    static
    type
    call( typename container_iterator< vec const >::type & it ) {
        return **it;
    }
};

} // namespace traits
} // namespace spirit
} // namespace boost



int
main() {
    vec v;
    v.push_back( ptr( new int( 1 ) ) );
    v.push_back( ptr( new int( 2 ) ) );
    v.push_back( ptr( new int( 3 ) ) );

    using namespace boost::spirit::karma;
    using boost::spirit::ascii::space;

    generate_delimited(
        std::ostream_iterator< char >( std::cout ),
        *int_,
        space,
        v
    );

    return 0;
}

以下是编译错误：

...patience...
...patience...
...found 1986 targets...
...updating 3 targets...
gcc.compile.c++ /home/john/Dev/Bio/bin/Bio/gcc-4.6/release/src/spirit/vector-of-ptrs.o
In file included from /home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/numeric/bool_policies.hpp:16:0,
from /home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/numeric/bool.hpp:29,
from /home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/numeric.hpp:13,
from /home/john/src/boost/boost_1_51_0/boost/spirit/home/karma.hpp:15,
from /home/john/src/boost/boost_1_51_0/boost/spirit/include/karma.hpp:16,
from src/spirit/vector-of-ptrs.cpp:1:
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/numeric/detail/numeric_utils.hpp: In static member function ‘static boost::shared_ptr<
        int> boost::spirit::traits::absolute_value<boost::shared_ptr<int>, void>::call(boost::shared_ptr<int>)’:
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/numeric/detail/numeric_utils.hpp:149:41:   instantiated from ‘boost::spirit::traits::absolute_value<boost::shared_ptr<int> >::ame boost
    ::spirit::traits::absolute_value<T>::type = boost::shared_ptr<int> boost::spirit::traits::get_absolute_value(boost::shared_ptr<int>)’
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/numeric/int.hpp:213:57:   instantiated from ‘static bool boost::spirit::karma::any_int_generator<
        int, boost::spirit::unused_type, boost::spirit::unused_type, 10u, false
    >::insert_int(boost::spirit::karma::detail::output_iterator<ostream_iterator<char>, mpl_::int_<0>, boost::spirit::unused_type> &, const boost::shared_ptr<int> &)’
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/numeric/int.hpp:242:39:   instantiated from ‘static bool boost::spirit::karma::any_int_generator<
        int, boost::spirit::unused_type, boost::spirit::unused_type, 10u, false
    >::generate(
        boost::spirit::karma::detail::output_iterator<ostream_iterator<char>, mpl_::int_<0>, boost::spirit::unused_type> &, boost::spirit::context<
            boost::fusion::cons<const vector<boost::shared_ptr<int> > &, boost::fusion::nil>, boost::spirit::locals<> > &, const boost::spirit::karma::any_space<boost::spirit::char_encoding::ascii> &
      , const boost::shared_ptr<int> &)’
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/detail/fail_function.hpp:36:62:   instantiated from ‘bool boost::spirit::karma::detail::fail_function<
        boost::spirit::karma::detail::output_iterator<ostream_iterator<char>, mpl_::int_<0>, boost::spirit::unused_type>, boost::spirit::context<
            boost::fusion::cons<const vector<boost::shared_ptr<int> > &, boost::fusion::nil>, boost::spirit::locals<> >, boost::spirit::karma::any_space<boost::spirit::char_encoding::ascii> >
    ::operator()(const boost::spirit::karma::any_int_generator<int, boost::spirit::unused_type, boost::spirit::unused_type, 10u, false> &, const boost::shared_ptr<int> &) const’
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/detail/pass_container.hpp:274:13:   instantiated from ‘bool boost::spirit::karma::detail::pass_container<
        boost::spirit::karma::detail::fail_function<
            boost::spirit::karma::detail::output_iterator<ostream_iterator<char>, mpl_::int_<0>, boost::spirit::unused_type>, boost::spirit::context<
                boost::fusion::cons<const vector<boost::shared_ptr<int> > &, boost::fusion::nil>, boost::spirit::locals<> >, boost::spirit::karma::any_space<boost::spirit::char_encoding::ascii> >,
        vector<boost::shared_ptr<int> >, boost::spirit::karma::detail::indirect_iterator<vector<boost::shared_ptr<int> >::const_iterator>, mpl_::bool_<false> 
    >::dispatch_container(const boost::spirit::karma::any_int_generator<int, boost::spirit::unused_type, boost::spirit::unused_type, 10u, false> &, mpl_::mpl_::bool_<false>) const’
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/detail/pass_container.hpp:321:61:   [ skipping 2 instantiation contexts ]
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/operator/kleene.hpp:53:32:   instantiated from ‘bool boost::spirit::karma::base_kleene<
        boost::spirit::karma::any_int_generator<int, boost::spirit::unused_type, boost::spirit::unused_type, 10u, false>, mpl_::bool_<false>, boost::spirit::karma::kleene<
            boost::spirit::karma::any_int_generator<int, boost::spirit::unused_type, boost::spirit::unused_type, 10u, false> > 
    >::generate_subject(
        boost::spirit::karma::detail::pass_container<
            boost::spirit::karma::detail::fail_function<
                boost::spirit::karma::detail::output_iterator<ostream_iterator<char>, mpl_::int_<0>, boost::spirit::unused_type>, boost::spirit::context<
                    boost::fusion::cons<const vector<boost::shared_ptr<int> > &, boost::fusion::nil>, boost::spirit::locals<> >, boost::spirit::karma::any_space<boost::spirit::char_encoding::ascii> >
          , vector<boost::shared_ptr<int> >, boost::spirit::karma::detail::indirect_iterator<vector<boost::shared_ptr<int> >::const_iterator>, mpl_::bool_<false> >, const vector<
            boost::shared_ptr<int> > &, mpl_::mpl_::bool_<false>) const’
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/operator/kleene.hpp:126:17:   instantiated from ‘bool boost::spirit::karma::base_kleene<
        boost::spirit::karma::any_int_generator<int, boost::spirit::unused_type, boost::spirit::unused_type, 10u, false>, mpl_::bool_<false>, boost::spirit::karma::kleene<
            boost::spirit::karma::any_int_generator<int, boost::spirit::unused_type, boost::spirit::unused_type, 10u, false> > 
    >::generate(
        boost::spirit::karma::detail::output_iterator<ostream_iterator<char>, mpl_::int_<0>, boost::spirit::unused_type> &, boost::spirit::context<
            boost::fusion::cons<const vector<boost::shared_ptr<int> > &, boost::fusion::nil>, boost::spirit::locals<> > &, const boost::spirit::karma::any_space<boost::spirit::char_encoding::ascii> &
      , const vector<boost::shared_ptr<int> > &) const’
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/generate.hpp:161:53:   instantiated from ‘bool boost::spirit::karma::generate_delimited(
        boost::spirit::karma::detail::output_iterator<ostream_iterator<char>, mpl_::int_<0> > &, const boost::proto::exprns_::expr<
            boost::proto::tagns_::tag::dereference, boost::proto::argsns_::list1<const boost::spirit::terminal<boost::spirit::tag::int_> &>, 1l> &, const boost::proto::exprns_::expr<
            boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l> &, boost::spirit
        ::karma::delimit_flag::enum_type, const vector<boost::shared_ptr<int> > &)’
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/generate.hpp:185:82:   instantiated from ‘bool boost::spirit::karma::generate_delimited(
        ostream_iterator<char> &, const boost::proto::exprns_::expr<boost::proto::tagns_::tag::dereference, boost::proto::argsns_::list1<const boost::spirit::terminal<boost::spirit::tag::int_> &>,
            1l> &, const boost::proto::exprns_::expr<
            boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l> &, boost::spirit
        ::karma::delimit_flag::enum_type, const vector<boost::shared_ptr<int> > &)’
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/generate.hpp:227:48:   instantiated from ‘bool boost::spirit::karma::generate_delimited(
        const ostream_iterator<char> &, const boost::proto::exprns_::expr<
            boost::proto::tagns_::tag::dereference, boost::proto::argsns_::list1<const boost::spirit::terminal<boost::spirit::tag::int_> &>, 1l> &, const boost::proto::exprns_::expr<
            boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0l> &, const vector<
            boost::shared_ptr<int> > &)’
src/spirit/vector-of-ptrs.cpp:46:2:   instantiated from here
/home/john/src/boost/boost_1_51_0/boost/spirit/home/karma/numeric/detail/numeric_utils.hpp:60:26: error: No match for ‘fabs(boost::shared_ptr<int> &)’

STL Decryptor reminder:
    Use the /cand:L option to see all suppressed template candidates

    "/home/john/src/stlfilt/gfilt"  -ftemplate-depth-128 -Wno-deprecated -Wno-unused -Wno-error -O3 -finline-functions -Wno-inline -Wall -fPIC -Wno-deprecated -Wno-unused -DBOOST_FILESYSTEM_VERSION=3 -DNDEBUG -DWITH_NONAMESPACES -DXML_LIBRARY  -I"../Bio" -I"../Hmm" -I"/home/john/src/boost/boost_1_51_0" -c -o "/home/john/Dev/Bio/bin/Bio/gcc-4.6/release/src/spirit/vector-of-ptrs.o" "src/spirit/vector-of-ptrs.cpp"

...failed gcc.compile.c++ /home/john/Dev/Bio/bin/Bio/gcc-4.6/release/src/spirit/vector-of-ptrs.o...
...removing /home/john/Dev/Bio/bin/Bio/gcc-4.6/release/src/spirit/vector-of-ptrs.o
...skipped <p/home/john/Dev/Bio/bin/Bio/gcc-4.6/release>spirit-vector-of-ptrs for lack of <p/home/john/Dev/Bio/bin/Bio/gcc-4.6/release>src/spirit/vector-of-ptrs.o...
...failed updating 1 target...
...skipped 1 target...

Answer 1

一些实验让我知道为什么没有实例化特殊化的原因，在预期的情况下：迭代器在生成器的 evalation 期间被包装（用karma::detail::indirect_iterator）某处表达

以下是适用于我的修复：

namespace boost {
namespace spirit {
namespace traits {

    // specialise how iterators into containers of pointers are dereferenced
    template <>
        struct deref_iterator< karma::detail::indirect_iterator<vec::const_iterator> >
    {
        typedef karma::detail::indirect_iterator<vec::const_iterator> It;
        typedef int type;

        static type call( It const & it ) {
            return **it;
        }
    };

} // namespace traits
} // namespace spirit
} // namespace boost