optimize iteration through collections and UDTs (#507)

the hot path involved many unnecessary SharedRefPtr's copies,
avoiding them improves performance

Author: vhavel

src/collection_iterator.cpp

@@ -27,15 +27,14 @@ bool CollectionIterator::next() {
 }
 
 bool CollectionIterator::decode_value() {
-  DataType::ConstPtr data_type;
   if (collection_->value_type() == CASS_VALUE_TYPE_MAP) {
-    data_type =
+    const DataType::ConstPtr& data_type =
         (index_ % 2 == 0) ? collection_->primary_data_type() : collection_->secondary_data_type();
+    value_ = decoder_.decode_value(data_type);
   } else {
-    data_type = collection_->primary_data_type();
+    value_ = decoder_.decode_value(collection_->primary_data_type());
   }
 
-  value_ = decoder_.decode_value(data_type);
   return value_.is_valid();
 }
 

src/ref_counted.hpp

@@ -87,6 +87,19 @@ class SharedRefPtr {
     return *this;
   }
 
+#if defined(__cpp_rvalue_references)
+  SharedRefPtr<T>& operator=(SharedRefPtr<T>&& ref) noexcept {
+    if (ptr_ != NULL) {
+      ptr_->dec_ref();
+    }
+    ptr_ = ref.ptr_;
+    ref.ptr_ = NULL;
+    return *this;
+  }
+
+  SharedRefPtr(SharedRefPtr<T>&& ref) noexcept : ptr_(ref.ptr_) { ref.ptr_ = NULL; }
+#endif
+
   ~SharedRefPtr() {
     if (ptr_ != NULL) {
       ptr_->dec_ref();

src/user_type_field_iterator.hpp

@@ -30,9 +30,9 @@ class UserTypeFieldIterator : public Iterator {
   UserTypeFieldIterator(const Value* user_type_value)
       : Iterator(CASS_ITERATOR_TYPE_USER_TYPE_FIELD)
       , decoder_(user_type_value->decoder()) {
-    UserType::ConstPtr user_type(user_type_value->data_type());
-    next_ = user_type->fields().begin();
-    end_ = user_type->fields().end();
+    const UserType& user_type = static_cast<const UserType&>(*user_type_value->data_type());
+    next_ = user_type.fields().begin();
+    end_ = user_type.fields().end();
   }
 
   virtual bool next();

src/value.cpp

@@ -199,11 +199,11 @@ Value::Value(const DataType::ConstPtr& data_type, Decoder decoder)
     , is_null_(false) {
   assert(!data_type->is_collection());
   if (data_type->is_tuple()) {
-    SharedRefPtr<const CompositeType> composite_type(data_type);
-    count_ = composite_type->types().size();
+    const CompositeType& composite_type = static_cast<const CompositeType&>(*data_type);
+    count_ = composite_type.types().size();
   } else if (data_type->is_user_type()) {
-    UserType::ConstPtr user_type(data_type);
-    count_ = user_type->fields().size();
+    const UserType& user_type = static_cast<const UserType&>(*data_type);
+    count_ = user_type.fields().size();
   } else {
     count_ = 0;
   }