Boost Spirit Karma multiple optionals

Question

I'm seeing an error that I'm not seeing the resolution to. First, the relevant code:

namespace C {

    struct RangeEntry {
        size_t byte;
        boost::optional<size_t> bit;
    };

    struct Range {
        RangeEntry firstPart;
        boost::optional<RangeEntry> secondPart;
        boost::optional<size_t> shift;
    };
}

BOOST_FUSION_ADAPT_STRUCT(
    C::RangeEntry,
    (size_t, byte)
    (boost::optional<size_t>, bit)
)

BOOST_FUSION_ADAPT_STRUCT(
    C::Range,
    (C::RangeEntry , firstPart)
    (boost::optional<C::RangeEntry> , secondPart)
    (boost::optional<size_t> , shift)
)

... Declare the rules ...

karma::rule<Iterator, C::Range()> range;
karma::rule<Iterator, C::RangeEntry()> range_part;

... Define rules ...

range_part %= no_delimit[ulong_ << -(lit(":") << ulong_)];
range %= no_delimit[range_part << -(lit("-") << range_part)] << -(lit("<<") << ulong_);

At the range %= part, I get the compile error

/usr/include/boost/spirit/home/karma/numeric/detail/numeric_utils.hpp:504:30: error:
invalid operands to binary expression 
('C::RangeEntry' and 'C::RangeEntry')
    return floor(num / spirit::traits::pow10<T>(exp));
                 ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I'm guessing it's trying to match a RangeEntry to the ulong_ rule, but I can't figure out why? What am I missing?

Answer 1

The no_delimit directive is regrouping your exposed fusion sequences. Note that the following does compile:

    range %= range_part << -(lit("-") << range_part) << -(lit("<<") << ulong_);

or even

    range %= no_delimit[range_part << -(lit("-") << range_part) << -(lit("<<") << ulong_)];

AFAICT the rules are defined without delimiter, so the no_delimit should be redundant here anyway.

---

I have "fantasized" a RangeEntry type just to make it a selfcontained sample:

#include <boost/fusion/adapted.hpp>
#include <boost/spirit/include/karma.hpp>

namespace karma = boost::spirit::karma;

namespace C {
    typedef std::pair<unsigned long, boost::optional<unsigned long> > RangeEntry;

    struct Range {
        RangeEntry firstPart;
        boost::optional<RangeEntry> secondPart;
        boost::optional<size_t> shift;
    };
}

BOOST_FUSION_ADAPT_STRUCT(
    C::Range,
    (C::RangeEntry , firstPart)
    (boost::optional<C::RangeEntry> , secondPart)
    (boost::optional<size_t> , shift)
    );

//... Declare the rules ...

int main()
{
    typedef char* Iterator;
    karma::rule<Iterator, C::Range()> range;
    karma::rule<Iterator, C::RangeEntry()> range_part;

    //... Define rules ...

    using namespace karma;
    range_part %= no_delimit[ulong_ << -(lit(":") << ulong_)];
    range %= no_delimit[range_part << -(lit("-") << range_part) << -(lit("<<") << ulong_)];
}