+
+// For boost::hash
+size_t hash_value(const SGPropertyNode& node);
+
+// Helper comparison and hash functions for common cases
+
+namespace simgear
+{
+namespace props
+{
+struct Compare
+{
+ bool operator()(const SGPropertyNode* lhs, const SGPropertyNode* rhs) const
+ {
+ return SGPropertyNode::compare(*lhs, *rhs);
+ }
+ bool operator()(SGPropertyNode_ptr lhs, const SGPropertyNode* rhs) const
+ {
+ return SGPropertyNode::compare(*lhs, *rhs);
+ }
+ bool operator()(const SGPropertyNode* lhs, SGPropertyNode_ptr rhs) const
+ {
+ return SGPropertyNode::compare(*lhs, *rhs);
+ }
+ bool operator()(SGPropertyNode_ptr lhs, SGPropertyNode_ptr rhs) const
+ {
+ return SGPropertyNode::compare(*lhs, *rhs);
+ }
+};
+
+struct Hash
+{
+ size_t operator()(const SGPropertyNode* node) const
+ {
+ return hash_value(*node);
+ }
+ size_t operator()(SGPropertyNode_ptr node) const
+ {
+ return hash_value(*node);
+ }
+};
+}
+}