Merge pull request #122 from d-frey/patch-1

exception-safe object creation, fixes #118

src/json.hpp.re2c

@@ -584,6 +584,17 @@ class basic_json
 
 
   private:
+    /// helper for exception-safe object creation
+    template<typename T, typename... Args>
+    static T* create( Args&&... args )
+    {
+        AllocatorType<T> alloc;
+        auto deleter = [&](T* object) { alloc.deallocate(object, 1); };
+        std::unique_ptr<T, decltype(deleter)> object(alloc.allocate(1), deleter);
+        alloc.construct(object.get(), std::forward<Args>(args)...);
+        return object.release();
+    }
+
     ////////////////////////
     // JSON value storage //
     ////////////////////////
@@ -625,25 +636,19 @@ class basic_json
 
                 case (value_t::object):
                 {
-                    AllocatorType<object_t> alloc;
+                    object = create<object_t>();
-                    object = alloc.allocate(1);
-                    alloc.construct(object);
                     break;
                 }
 
                 case (value_t::array):
                 {
-                    AllocatorType<array_t> alloc;
+                    array = create<array_t>();
-                    array = alloc.allocate(1);
-                    alloc.construct(array);
                     break;
                 }
 
                 case (value_t::string):
                 {
-                    AllocatorType<string_t> alloc;
+                    string = create<string_t>("");
-                    string = alloc.allocate(1);
-                    alloc.construct(string, "");
                     break;
                 }
 
@@ -670,25 +675,19 @@ class basic_json
         /// constructor for strings
         json_value(const string_t& value)
         {
-            AllocatorType<string_t> alloc;
+            string = create<string_t>(value);
-            string = alloc.allocate(1);
-            alloc.construct(string, value);
         }
 
         /// constructor for objects
         json_value(const object_t& value)
         {
-            AllocatorType<object_t> alloc;
+            object = create<object_t>(value);
-            object = alloc.allocate(1);
-            alloc.construct(object, value);
         }
 
         /// constructor for arrays
         json_value(const array_t& value)
         {
-            AllocatorType<array_t> alloc;
+            array = create<array_t>(value);
-            array = alloc.allocate(1);
-            alloc.construct(array, value);
         }
     };
 
@@ -892,11 +891,9 @@ class basic_json
     basic_json(const CompatibleObjectType& value)
         : m_type(value_t::object)
     {
-        AllocatorType<object_t> alloc;
-        m_value.object = alloc.allocate(1);
         using std::begin;
         using std::end;
-        alloc.construct(m_value.object, begin(value), end(value));
+        m_value.object = create<object_t>(begin(value), end(value));
     }
 
     /*!
@@ -953,11 +950,9 @@ class basic_json
     basic_json(const CompatibleArrayType& value)
         : m_type(value_t::array)
     {
-        AllocatorType<array_t> alloc;
-        m_value.array = alloc.allocate(1);
         using std::begin;
         using std::end;
-        alloc.construct(m_value.array, begin(value), end(value));
+        m_value.array = create<array_t>(begin(value), end(value));
     }
 
     /*!
@@ -1315,9 +1310,7 @@ class basic_json
         {
             // the initializer list describes an array -> create array
             m_type = value_t::array;
-            AllocatorType<array_t> alloc;
+            m_value.array = create<array_t>(std::move(init));
-            m_value.array = alloc.allocate(1);
-            alloc.construct(m_value.array, std::move(init));
         }
     }
 
@@ -1416,9 +1409,7 @@ class basic_json
     basic_json(size_type count, const basic_json& value)
         : m_type(value_t::array)
     {
-        AllocatorType<array_t> alloc;
+        m_value.array = create<array_t>(count, value);
-        m_value.array = alloc.allocate(1);
-        alloc.construct(m_value.array, count, value);
     }
 
     /*!
@@ -1514,17 +1505,13 @@ class basic_json
 
             case value_t::object:
             {
-                AllocatorType<object_t> alloc;
+                m_value.object = create<object_t>(first.m_it.object_iterator, last.m_it.object_iterator);
-                m_value.object = alloc.allocate(1);
-                alloc.construct(m_value.object, first.m_it.object_iterator, last.m_it.object_iterator);
                 break;
             }
 
             case value_t::array:
             {
-                AllocatorType<array_t> alloc;
+                m_value.array = create<array_t>(first.m_it.array_iterator, last.m_it.array_iterator);
-                m_value.array = alloc.allocate(1);
-                alloc.construct(m_value.array, first.m_it.array_iterator, last.m_it.array_iterator);
                 break;
             }
 
@@ -2595,9 +2582,7 @@ class basic_json
         if (m_type == value_t::null)
         {
             m_type = value_t::array;
-            AllocatorType<array_t> alloc;
+            m_value.array = create<array_t>();
-            m_value.array = alloc.allocate(1);
-            alloc.construct(m_value.array);
         }
 
         // [] only works for arrays
@@ -2667,9 +2652,7 @@ class basic_json
         if (m_type == value_t::null)
         {
             m_type = value_t::object;
-            AllocatorType<object_t> alloc;
+            m_value.object = create<object_t>();
-            m_value.object = alloc.allocate(1);
-            alloc.construct(m_value.object);
         }
 
         // [] only works for objects