From cc78a5de788d6e30c21fccfa1a505c6d01eee5df Mon Sep 17 00:00:00 2001
From: Artem Pavlenko <artem@mapnik.org>
Date: Tue, 12 May 2020 12:14:18 +0100
Subject: [PATCH] Fix for boost < 1.70.0 (ref #4143)

---
 include/mapnik/json/feature_generator_grammar.hpp | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/mapnik/json/feature_generator_grammar.hpp b/include/mapnik/json/feature_generator_grammar.hpp
index 5783e5344..5df0cf938 100644
--- a/include/mapnik/json/feature_generator_grammar.hpp
+++ b/include/mapnik/json/feature_generator_grammar.hpp
@@ -91,15 +91,23 @@ BOOST_FUSION_ADAPT_ADT(
     (mapnik::kv_store const, mapnik::kv_store const, mapnik::kv_store(obj), /**/))
 
 namespace mapnik { namespace json {
+namespace detail {
+template <typename T>
+#if BOOST_VERSION >= 107000
+struct attribute_type { using type = T();};
+#else
+struct attribute_type { using type = T const&();};
+#endif
+}
 
 namespace karma = boost::spirit::karma;
 
 template <typename OutputIterator, typename FeatureType>
 struct feature_generator_grammar :
-        karma::grammar<OutputIterator, FeatureType const&()>
+        karma::grammar<OutputIterator, typename detail::attribute_type<FeatureType>::type>
 {
     feature_generator_grammar();
-    karma::rule<OutputIterator, FeatureType const&()> feature;
+    karma::rule<OutputIterator, typename detail::attribute_type<FeatureType>::type> feature;
     geometry_generator_grammar<OutputIterator, mapnik::geometry::geometry<double>> geometry;
     properties_generator_grammar<OutputIterator, mapnik::kv_store> properties;
 };