Make Node move constructor and assignment operator noexcept (#809)

Move constructor:
 * m_isValid    (bool)                 exchange(rhs.m_isValid, true)
 * m_invalidKey (std::string)          std::move()
 * m_pMemory    (shared_memory_holder) std::move()
 * m_pNode      (node*)                exchange(rhs.m_pNode, nullptr)

 This leaves the moved-from Node as if it was just default constructed.

Move assignment:
 A temporary Node is move constructed (using the above) leaving the moved-from
 Node as if it was just default constructed.

*this then assigns the temporary, using AssignNodeDetail() directly to avoid
a second self-assignment check.

Signed-off-by: Ted Lyngmo <ted@lyncon.se>

Author: TedLyngmo

include/yaml-cpp/node/impl.h

@@ -12,11 +12,28 @@
 #include "yaml-cpp/node/detail/node.h"
 #include "yaml-cpp/node/iterator.h"
 #include "yaml-cpp/node/node.h"
+#include "yaml-cpp/noexcept.h"
 #include <sstream>
 #include <string>
+#include <utility>
 
 namespace YAML {
-inline Node::Node()
+namespace detail {
+#if __cplusplus >= 201402L
+using ::std::exchange;
+#else
+template<class T, class U = T>
+T exchange(T& obj, U&& new_value) {
+  T old_value = std::move(obj);
+  obj = std::forward<U>(new_value);
+  return old_value;
+}
+#endif
+}  // namespace detail
+}  // namespace YAML
+
+namespace YAML {
+inline Node::Node() YAML_CPP_NOEXCEPT
     : m_isValid(true), m_invalidKey{}, m_pMemory(nullptr), m_pNode(nullptr) {}
 
 inline Node::Node(NodeType::value type)
@@ -44,6 +61,13 @@ inline Node::Node(const detail::iterator_value& rhs)
 
 inline Node::Node(const Node& rhs) = default;
 
+inline Node::Node(Node&& rhs) YAML_CPP_NOEXCEPT
+    : m_isValid(detail::exchange(rhs.m_isValid, true)),
+      m_invalidKey(std::move(rhs.m_invalidKey)),
+      m_pMemory(std::move(rhs.m_pMemory)),
+      m_pNode(detail::exchange(rhs.m_pNode, nullptr)) {
+}
+
 inline Node::Node(Zombie)
     : m_isValid(false), m_invalidKey{}, m_pMemory{}, m_pNode(nullptr) {}
 
@@ -188,6 +212,13 @@ inline void Node::SetStyle(EmitterStyle::value style) {
 }
 
 // assignment
+inline bool Node::CheckValid(const Node& rhs) const YAML_CPP_NOEXCEPT {
+  return
+    m_isValid && rhs.m_isValid &&
+    m_pNode != nullptr && rhs.m_pNode != nullptr &&
+    !m_pNode->is(*rhs.m_pNode);
+}
+
 inline bool Node::is(const Node& rhs) const {
   if (!m_isValid || !rhs.m_isValid)
     throw InvalidNode(m_invalidKey);
@@ -209,6 +240,16 @@ inline Node& Node::operator=(const Node& rhs) {
   return *this;
 }
 
+inline Node& Node::operator=(Node&& rhs) YAML_CPP_NOEXCEPT {
+  if (!CheckValid(rhs))
+    return *this;
+
+  Node tmp(std::move(rhs));
+  AssignNodeDetail(tmp);
+
+  return *this;
+}
+
 inline void Node::reset(const YAML::Node& rhs) {
   if (!m_isValid || !rhs.m_isValid)
     throw InvalidNode(m_invalidKey);
@@ -258,6 +299,10 @@ inline void Node::AssignNode(const Node& rhs) {
     return;
   }
 
+  AssignNodeDetail(rhs);
+}
+
+inline void Node::AssignNodeDetail(const Node& rhs) YAML_CPP_NOEXCEPT {
   m_pNode->set_ref(*rhs.m_pNode);
   m_pMemory->merge(*rhs.m_pMemory);
   m_pNode = rhs.m_pNode;

include/yaml-cpp/node/node.h

@@ -16,6 +16,7 @@
 #include "yaml-cpp/node/detail/iterator_fwd.h"
 #include "yaml-cpp/node/ptr.h"
 #include "yaml-cpp/node/type.h"
+#include "yaml-cpp/noexcept.h"
 
 namespace YAML {
 namespace detail {
@@ -41,12 +42,13 @@ class YAML_CPP_API Node {
   using iterator = YAML::iterator;
   using const_iterator = YAML::const_iterator;
 
-  Node();
+  Node() YAML_CPP_NOEXCEPT;
   explicit Node(NodeType::value type);
   template <typename T>
   explicit Node(const T& rhs);
   explicit Node(const detail::iterator_value& rhs);
   Node(const Node& rhs);
+  Node(Node&& rhs) YAML_CPP_NOEXCEPT;
   ~Node();
 
   YAML::Mark Mark() const;
@@ -77,10 +79,12 @@ class YAML_CPP_API Node {
   void SetStyle(EmitterStyle::value style);
 
   // assignment
+  bool CheckValid(const Node& rhs) const YAML_CPP_NOEXCEPT;
   bool is(const Node& rhs) const;
   template <typename T>
   Node& operator=(const T& rhs);
   Node& operator=(const Node& rhs);
+  Node& operator=(Node&& rhs) YAML_CPP_NOEXCEPT;
   void reset(const Node& rhs = Node());
 
   // size/iterator
@@ -128,6 +132,7 @@ class YAML_CPP_API Node {
 
   void AssignData(const Node& rhs);
   void AssignNode(const Node& rhs);
+  void AssignNodeDetail(const Node& rhs) YAML_CPP_NOEXCEPT;
 
  private:
   bool m_isValid;