work around clang bug in visit

Author: grisumbras

include/boost/json/impl/visit.hpp

@@ -49,16 +49,30 @@ visit(
     value const& jv) -> decltype(
         static_cast<Visitor&&>(v)( std::declval<std::nullptr_t const&>() ) )
 {
+    detail::scalar const& sc = detail::access::get_scalar(jv);
     switch(jv.kind())
     {
     default: // unreachable()?
     case kind::string:  return static_cast<Visitor&&>(v)( jv.get_string() );
     case kind::array:   return static_cast<Visitor&&>(v)( jv.get_array() );
     case kind::object:  return static_cast<Visitor&&>(v)( jv.get_object() );
-    case kind::bool_:   return static_cast<Visitor&&>(v)( detail::access::get_scalar(jv).b );
-    case kind::int64:   return static_cast<Visitor&&>(v)( detail::access::get_scalar(jv).i );
-    case kind::uint64:  return static_cast<Visitor&&>(v)( detail::access::get_scalar(jv).u );
-    case kind::double_: return static_cast<Visitor&&>(v)( detail::access::get_scalar(jv).d );
+    // local variables work around a bug in older clangs
+    case kind::bool_: {
+        bool const& b = sc.b;
+        return static_cast<Visitor&&>(v)(b);
+    }
+    case kind::int64: {
+        std::int64_t const& i = sc.i;
+        return static_cast<Visitor&&>(v)(i);
+    }
+    case kind::uint64: {
+        std::uint64_t const& u =  sc.u;
+        return static_cast<Visitor&&>(v)(u);
+    }
+    case kind::double_: {
+        double const& d = sc.d;
+        return static_cast<Visitor&&>(v)(d);
+    }
     case kind::null: {
         auto const& np = detail::stable_np;
         return static_cast<Visitor&&>(v)(np) ;

test/visit.cpp

@@ -29,6 +29,10 @@ struct visitor_checker<value const&>
     operator()(std::nullptr_t const& n) const
     { return {kind::null, &n}; }
 
+    std::pair<kind, void const*>
+    operator()(bool&)
+    { BOOST_TEST_FAIL(); return {(kind)50, nullptr}; }
+
     std::pair<kind, void const*>
     operator()(bool const& b) const
     { return {kind::bool_, &b}; }
@@ -60,17 +64,17 @@ struct visitor_checker<value const&>
     template<class T>
     std::pair<kind, void const*>
     operator()(T&&) const&
-    { return {(kind)1000000, nullptr}; }
+    { return {(kind)40, nullptr}; }
 
     template<class T>
     std::pair<kind, void const*>
     operator()(T&&) &
-    { return {(kind)1000000, nullptr}; }
+    { return {(kind)41, nullptr}; }
 
     template<class T>
     std::pair<kind, void const*>
     operator()(T&&) &&
-    { return {(kind)1000000, nullptr}; }
+    { return {(kind)42, nullptr}; }
 };
 
 template<>
@@ -115,17 +119,17 @@ struct visitor_checker<value&>
     template<class T>
     std::pair<kind, void const*>
     operator()(T&&) const&
-    { return {(kind)1000000, nullptr}; }
+    { return {(kind)40, nullptr}; }
 
     template<class T>
     std::pair<kind, void const*>
     operator()(T&&) &
-    { return {(kind)1000000, nullptr}; }
+    { return {(kind)41, nullptr}; }
 
     template<class T>
     std::pair<kind, void const*>
     operator()(T&&) &&
-    { return {(kind)1000000, nullptr}; }
+    { return {(kind)42, nullptr}; }
 };
 
 template<>
@@ -170,17 +174,17 @@ struct visitor_checker<value&&>
     template<class T>
     std::pair<kind, void const*>
     operator()(T&&) const&
-    { return {(kind)1000000, nullptr}; }
+    { static_assert( !std::is_same<T, T>::value, "" ); return {(kind)40, nullptr}; }
 
     template<class T>
     std::pair<kind, void const*>
     operator()(T&&) &
-    { return {(kind)1000000, nullptr}; }
+    { static_assert( !std::is_same<T, T>::value, "" ); return {(kind)41, nullptr}; }
 
     template<class T>
     std::pair<kind, void const*>
     operator()(T&&) &&
-    { return {(kind)1000000, nullptr}; }
+    { static_assert( !std::is_same<T, T>::value, "" ); return {(kind)42, nullptr}; }
 };
 
 class visit_test
@@ -288,6 +292,7 @@ class visit_test
 
     void run()
     {
+        value const jv;
         visitor_ref_tester()();
 
         BOOST_TEST_CHECKPOINT();