Adding swap() for GenericMember

Author: miloyip

example/sortkeys/sortkeys.cpp

@@ -17,10 +17,7 @@ static void printIt(const Value &doc) {
 }
 
 struct NameComparator {
-    bool operator()(
-        const GenericMember<UTF8<>, MemoryPoolAllocator<> > &lhs,
-        const GenericMember<UTF8<>, MemoryPoolAllocator<> > &rhs) const
-    {
+    bool operator()(const Value::Member &lhs, const Value::Member &rhs) const {
         return (strcmp(lhs.name.GetString(), rhs.name.GetString()) < 0);
     }
 };

include/rapidjson/document.h

@@ -66,6 +66,12 @@ template <typename Encoding, typename Allocator>
 struct GenericMember { 
     GenericValue<Encoding, Allocator> name;     //!< name of member (must be a string)
     GenericValue<Encoding, Allocator> value;    //!< value of member.
+
+    // swap() for std::sort() and other potential use in STL.
+    friend inline void swap(GenericMember& a, GenericMember& b) RAPIDJSON_NOEXCEPT {
+        a.name.Swap(b.name);
+        a.value.Swap(b.value);
+    }
 };
 
 ///////////////////////////////////////////////////////////////////////////////