add GenericDocument<>::Swap

See #368.

include/rapidjson/document.h

@@ -1803,6 +1803,22 @@ public:
     }
 #endif
 
+    //! Exchange the contents of this document with those of another.
+    /*!
+        \param other Another document.
+        \note Constant complexity.
+        \see GenericValue::Swap
+    */
+    GenericDocument& Swap(GenericDocument& rhs) RAPIDJSON_NOEXCEPT {
+        using std::swap;
+        ValueType::Swap(rhs);
+        stack_.Swap(rhs.stack_);
+        swap(allocator_, rhs.allocator_);
+        swap(ownAllocator_, rhs.ownAllocator_);
+        swap(parseResult_, rhs.parseResult_);
+        return *this;
+    }
+
     //!@name Parse from stream
     //!@{
 

include/rapidjson/internal/stack.h

@@ -15,6 +15,8 @@
 #ifndef RAPIDJSON_INTERNAL_STACK_H_
 #define RAPIDJSON_INTERNAL_STACK_H_
 
+#include <algorithm> // std::swap
+
 #include "../rapidjson.h"
 
 RAPIDJSON_NAMESPACE_BEGIN
@@ -81,6 +83,17 @@ public:
     }
 #endif
 
+    void Swap(Stack& rhs) RAPIDJSON_NOEXCEPT {
+        using std::swap;
+
+        swap(allocator_, rhs.allocator_);
+        swap(ownAllocator_, rhs.ownAllocator_);
+        swap(stack_, rhs.stack_);
+        swap(stackTop_, rhs.stackTop_);
+        swap(stackEnd_, rhs.stackEnd_);
+        swap(initialCapacity_, rhs.initialCapacity_);
+    }
+
     void Clear() { stackTop_ = stack_; }
 
     void ShrinkToFit() { 

test/unittest/documenttest.cpp

@@ -202,7 +202,8 @@ TEST(Document, Swap) {
     o.SetObject().AddMember("a", 1, a);
 
     // Swap between Document and Value
-    d1.Swap(o);
+    // d1.Swap(o); // doesn't compile
+    o.Swap(d1);
     EXPECT_TRUE(d1.IsObject());
     EXPECT_TRUE(o.IsArray());
 
@@ -212,8 +213,19 @@ TEST(Document, Swap) {
     d1.Swap(d2);
     EXPECT_TRUE(d1.IsArray());
     EXPECT_TRUE(d2.IsObject());
+    EXPECT_EQ(&d2.GetAllocator(), &a);
+
+    // reset value
+    Value().Swap(d1);
+    EXPECT_TRUE(d1.IsNull());
+
+    // reset document, including allocator
+    Document().Swap(d2);
+    EXPECT_TRUE(d2.IsNull());
+    EXPECT_NE(&d2.GetAllocator(), &a);
 }
 
+
 // This should be slow due to assignment in inner-loop.
 struct OutputStringStream : public std::ostringstream {
     typedef char Ch;