add and use simplified "internal::Swap"

This avoids the dependency on the <algorithm> header, as suggested by
@miloyip in #376.

include/rapidjson/document.h

@@ -1810,12 +1810,11 @@ public:
         \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_);
+        internal::Swap(allocator_, rhs.allocator_);
+        internal::Swap(ownAllocator_, rhs.ownAllocator_);
+        internal::Swap(parseResult_, rhs.parseResult_);
         return *this;
     }
 

include/rapidjson/internal/stack.h

@@ -15,9 +15,8 @@
 #ifndef RAPIDJSON_INTERNAL_STACK_H_
 #define RAPIDJSON_INTERNAL_STACK_H_
 
-#include <algorithm> // std::swap
-
 #include "../rapidjson.h"
+#include "swap.h"
 
 RAPIDJSON_NAMESPACE_BEGIN
 namespace internal {
@@ -84,14 +83,12 @@ 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_);
+        internal::Swap(allocator_, rhs.allocator_);
+        internal::Swap(ownAllocator_, rhs.ownAllocator_);
+        internal::Swap(stack_, rhs.stack_);
+        internal::Swap(stackTop_, rhs.stackTop_);
+        internal::Swap(stackEnd_, rhs.stackEnd_);
+        internal::Swap(initialCapacity_, rhs.initialCapacity_);
     }
 
     void Clear() { stackTop_ = stack_; }

include/rapidjson/internal/swap.h

+// Tencent is pleased to support the open source community by making RapidJSON available.
+//
+// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
+//
+// Licensed under the MIT License (the "License"); you may not use this file except
+// in compliance with the License. You may obtain a copy of the License at
+//
+// http://opensource.org/licenses/MIT
+//
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+#ifndef RAPIDJSON_INTERNAL_SWAP_H_
+#define RAPIDJSON_INTERNAL_SWAP_H_
+
+#include "../rapidjson.h"
+
+RAPIDJSON_NAMESPACE_BEGIN
+namespace internal {
+
+//! Custom swap() to avoid dependency on C++ <algorith> header
+/*! \tparam T Type of the arguments to swap, should be instantiated with primitive C++ types only.
+    \note This has the same semantics as std::swap().
+*/
+template <typename T>
+inline void Swap(T& a, T& b) RAPIDJSON_NOEXCEPT {
+    T tmp = a;
+        a = b;
+        b = tmp;
+}
+
+} // namespace internal
+RAPIDJSON_NAMESPACE_END
+
+#endif // RAPIDJSON_INTERNAL_SWAP_H_