add free inline `swap` functions

include/rapidjson/document.h

@@ -660,6 +660,8 @@ public:
         return *this;
     }
 
+    friend inline void swap(GenericValue& a, GenericValue& b) RAPIDJSON_NOEXCEPT { a.Swap(b); }
+
     //! Prepare Value for move semantics
     /*! \return *this */
     GenericValue& Move() RAPIDJSON_NOEXCEPT { return *this; }
@@ -1818,6 +1820,8 @@ public:
         return *this;
     }
 
+    friend inline void swap(GenericDocument& a, GenericDocument& b) RAPIDJSON_NOEXCEPT { a.Swap(b); }
+
     //!@name Parse from stream
     //!@{
 

test/unittest/documenttest.cpp

@@ -19,6 +19,7 @@
 #include "rapidjson/encodedstream.h"
 #include "rapidjson/stringbuffer.h"
 #include <sstream>
+#include <algorithm>
 
 using namespace rapidjson;
 
@@ -223,6 +224,17 @@ TEST(Document, Swap) {
     Document().Swap(d2);
     EXPECT_TRUE(d2.IsNull());
     EXPECT_NE(&d2.GetAllocator(), &a);
+
+    // testing std::swap compatibility
+    d1.SetBool(true);
+    using std::swap;
+    swap(d1, d2);
+    EXPECT_TRUE(d1.IsNull());
+    EXPECT_TRUE(d2.IsTrue());
+
+    swap(o, d2);
+    EXPECT_TRUE(o.IsTrue());
+    EXPECT_TRUE(d2.IsArray());
 }
 
 

test/unittest/valuetest.cpp

@@ -272,6 +272,12 @@ TEST(Value, Swap) {
     EXPECT_TRUE(v1.IsObject());
     EXPECT_TRUE(v2.IsInt());
     EXPECT_EQ(1234, v2.GetInt());
+
+    // testing std::swap compatibility
+    using std::swap;
+    swap(v1, v2);
+    EXPECT_TRUE(v1.IsInt());
+    EXPECT_TRUE(v2.IsObject());
 }
 
 TEST(Value, Null) {