diff options
Diffstat (limited to 'boost/spirit/home/karma/detail/extract_from.hpp')
| -rw-r--r-- | boost/spirit/home/karma/detail/extract_from.hpp | 45 |
1 files changed, 25 insertions, 20 deletions
diff --git a/boost/spirit/home/karma/detail/extract_from.hpp b/boost/spirit/home/karma/detail/extract_from.hpp index 558d056352..5499212824 100644 --- a/boost/spirit/home/karma/detail/extract_from.hpp +++ b/boost/spirit/home/karma/detail/extract_from.hpp @@ -44,40 +44,45 @@ namespace boost { namespace spirit { namespace traits } // This is the default case: the plain attribute values - template <typename Attribute, typename Exposed, typename Enable/*= void*/> - struct extract_from_attribute + template <typename Attribute, typename Exposed + , bool IsOneElemSeq = traits::one_element_sequence<Attribute>::value> + struct extract_from_attribute_base { - typedef typename traits::one_element_sequence<Attribute>::type - is_one_element_sequence; - - typedef typename mpl::eval_if< - is_one_element_sequence - , detail::value_at_c<Attribute, 0> - , mpl::identity<Attribute const&> - >::type type; + typedef Attribute const& type; template <typename Context> - static type call(Attribute const& attr, Context&, mpl::false_) + static type call(Attribute const& attr, Context&) { return attr; } + }; - // This handles the case where the attribute is a single element fusion - // sequence. We silently extract the only element and treat it as the - // attribute to generate output from. - template <typename Context> - static type call(Attribute const& attr, Context& ctx, mpl::true_) - { - return extract_from<Exposed>(fusion::at_c<0>(attr), ctx); - } + // This handles the case where the attribute is a single element fusion + // sequence. We silently extract the only element and treat it as the + // attribute to generate output from. + template <typename Attribute, typename Exposed> + struct extract_from_attribute_base<Attribute, Exposed, true> + { + typedef typename remove_const< + typename remove_reference< + typename fusion::result_of::at_c<Attribute, 0>::type + >::type + >::type elem_type; + + typedef typename result_of::extract_from<Exposed, elem_type>::type type; template <typename Context> static type call(Attribute const& attr, Context& ctx) { - return call(attr, ctx, is_one_element_sequence()); + return extract_from<Exposed>(fusion::at_c<0>(attr), ctx); } }; + template <typename Attribute, typename Exposed, typename Enable/*= void*/> + struct extract_from_attribute + : extract_from_attribute_base<Attribute, Exposed> + {}; + // This handles optional attributes. template <typename Attribute, typename Exposed> struct extract_from_attribute<boost::optional<Attribute>, Exposed> |