Add null_handler

include/boost/json/detail/parse_into.hpp

@@ -255,6 +255,41 @@ template<class V, class P> class bool_handler: public handler_error_base<error::
     }
 };
 
+// null_handler
+
+template<class V, class P> class null_handler: public handler_error_base<error::not_null>
+{
+private:
+
+    V * value_;
+    P * parent_;
+
+public:
+
+    null_handler( null_handler const& ) = delete;
+    null_handler& operator=( null_handler const& ) = delete;
+
+public:
+
+    null_handler( V* v, P* p ): value_( v ), parent_( p )
+    {
+    }
+
+    bool on_null( error_code& )
+    {
+        *value_ = {};
+
+        parent_->signal_value();
+        return true;
+    }
+
+    bool on_array_end( std::size_t, error_code& )
+    {
+        parent_->signal_end();
+        return true;
+    }
+};
+
 // forward declarations
 
 template<class V, class P> class sequence_handler;
@@ -317,6 +352,7 @@ template<class T> struct is_described_struct<T, decltype((void)boost::describe::
 
 template<class V, class P> using get_handler = boost::mp11::mp_cond<
 
+    std::is_same<V, std::nullptr_t>, null_handler<V, P>,
     std::is_same<V, bool>, bool_handler<V, P>,
     std::is_integral<V>, integral_handler<V, P>,
     std::is_floating_point<V>, floating_point_handler<V, P>,

test/parse_into.cpp

@@ -69,6 +69,11 @@ class parse_into_test
         BOOST_TEST( !ec.failed() ) && BOOST_TEST( t1 == t2 );
     }
 
+    void testNull()
+    {
+        testParseInto( nullptr );
+    }
+
     void testBoolean()
     {
         testParseInto( false );
@@ -107,6 +112,8 @@ class parse_into_test
 
     void testSequence()
     {
+        testParseInto<std::vector<std::nullptr_t>>( { nullptr, nullptr } );
+
         testParseInto< std::vector<bool> >( {} );
         testParseInto< std::vector<bool> >( { true, false } );
 
@@ -176,6 +183,7 @@ class parse_into_test
 
     void run()
     {
+        testNull();
         testBoolean();
         testIntegral();
         testFloatingPoint();