此问题确定不可复制的类型不能与Boost变体一起使用
Tree
上课
template <class T = int>
class Tree{
private:
class TreeNode{
public:
std::unique_ptr Nodes
Move constructors and move assignment + other public members
private:
TreeNode(const TreeNode &other); (= delete not supported on compiler)
TreeNode& operator=(const TreeNode &rhs); (= delete not supported on compiler)
}; // End Tree Node Class Definition
Tree(const Tree &other); (= delete not supported on compiler)
Tree& operator=(const Tree &rhs); (= delete not supported on compiler)
public:
Move constructors and move assignment + other public members
};
TreeVisitor
上课
class TreeVisitor : public boost::static_visitor<bool> {
public:
TreeVisitor() {}
bool operator() (BinarySearchTree<std::string>& tree) const {
return searchTree.load(tree);
}
private:
};
TreeVariant
typedef boost::variant<Tree<std::string>, Tree<int>> TreeVariant;
TreeVariant tree;
Tree<std::string> stringTree;
Tree<int> intTree;
按如下方式应用Visitors
tree = intSearchTree;
boost::apply_visitor(TreeVisitor(), tree)
还使用boost :: bind作为所需参数
boost::bind(TreeVisitor(), tree, val, keyIndex);
类型
的编译器错误error C2248: 'Tree<T>::Tree' : cannot access private member declared in class 'Tree<T>' <----- related to private copy constructor in Tree (not TreeNode)
tree = stringTree; <------- error related to assignment
Tree
正确编译并已经过测试。如何解决这些与尝试获取Tree
类副本相关的编译错误,因为std::unique_ptr
这是不可能的?
SSCCE
<class T = int>
class Tree{
private:
class TreeNode{
public:
TreeNode() {}
~TreeNode() {}
TreeNode(TreeNode &&other) :
key(other.key), index(other.index), left(std::move(other.left)), right(std::move(other.right))
{
key = index = left = right = nullptr;
}
TreeNode &operator=(BTreeNode &&rhs)
{
if(this != &rhs)
{
key = rhs.key; index = rhs.index;
left = std::move(rhs.left); right = std::move(rhs.right);
rhs.key = rhs.index = rhs.left = rhs.right = nullptr;
}
return *this;
}
TreeNode(const T &new_key, const T &new_index) :
key(new_key), index(new_index), left(nullptr), right(nullptr) {}
friend class Tree;
private:
TreeNode(const BinarySearchTreeNode &other);
TreeNode& operator=(const BinarySearchTreeNode &rhs);
std::unique_ptr<TreeNode> left;
std::unique_ptr<TreeNode> right;
}; // End Tree Node Class Definition
std::unique_ptr<TreeNode> root;
BinarySearchTree(const BinarySearchTree &other);
BinarySearchTree& operator=(const BinarySearchTree &rhs);
public:
Tree() : root(nullptr), flag(false), run(true), leftCount(0), rightCount(0) {}
~Tree() {}
Tree(BinarySearchTree &&other) : root(std::move(other.root)) { other.root = nullptr; }
Tree &operator=(BinarySearchTree &&rhs)
{
if(this != &rhs)
{
root = std::move(rhs.root);
rhs.root = nullptr;
}
return *this;
}
};
使用示例:
bool delete_(){
while(!instances.empty()){
// grab first instance
keyIndex = instances.at(0);
// compute end of the tuple to delete
endIndex = keyIndex + sizeToDelete;
// read the first attribute
try{
temp = boost::trim_copy(dataFile->readData(keyIndex, domainSize));
}
catch (std::exception &e){
printw("Error reading from the data file");
}
// delete tuple from data file
if(!dataFile->deleteTuple(keyIndex, endIndex)){
printw("Error attempting to remove tuple");
if (writer_ != nullptr)
writer_ << "Error attempting to remove tuple";
try{
printw("%s");
// close catalog and search file
}
catch (std::exception &e){
e.what();
}
// close data file
dataFile->closeFile();
return false;
}
try{
int val = boost::lexical_cast<int>(temp);
searchTree = intSearchTree;
boost::bind(BinarySearchTreeVisitor(), searchTree, val, keyIndex);
// delete key index from the index file
if (!boost::apply_visitor(BinarySearchTreeVisitor(), searchTree)){
printw("No index present in index file");
try{
printw(" ");
}
catch (std::exception &e){
}
// close data file
dataFile->closeFile();
return false;
}
}
catch(boost::bad_lexical_cast &e){
/*
* Must be a std::string --- wow who knew
*/
searchTree = stringSearchTree;
boost::bind(BinarySearchTreeVisitor(), searchTree, temp, keyIndex);
// delete key index from the index file
if (!boost::apply_visitor(BinarySearchTreeVisitor(), searchTree)){
printw("No index present in index file");
try{
printw(" ");
// close catalog and search file
}
catch (std::exception &e){
e.what();
}
// close data file
dataFile->closeFile();
return false;
}
}
// clean up the index file
boost::bind(BinarySearchTreeVisitor(), searchTree, keyIndex, sizeToDelete);
boost::apply_visitor(BinarySearchTreeVisitor(), searchTree);
instances.erase(instances.begin());
for(int i= 0; i < instances.size(); i++){
instances.assign(i, instances.at(i) -
sizeToDelete);
}
}
}
答案 0 :(得分:6)
关于对boost::bind()
的调用,在通过引用传递对象时,应使用boost::ref()
,该函数模板按值接受相应的参数,否则 copy 将尝试(在这种情况下导致编译器错误,因为复制构造函数不可访问):
boost::bind(TreeVisitor(), boost::ref(tree), val, keyIndex);
// ^^^^^^^^^^^^^^^^
但是,这里存在一个更大的问题:boost::variant
只能包含可复制构造的类型。来自Boost.Variant online documentation:
对有界类型的要求如下:
CopyConstructible
[20.1.3]。Destructor坚持无抛出异常安全保证。
在变体模板实例化时完成。 (有关接受不完整类型的类型包装器,请参阅
boost::recursive_wrapper<T>
以启用递归变体类型。)指定为
variant
的模板参数的每种类型都必须至少满足上述要求。 [...]
答案 1 :(得分:1)
using Mixed = boost::variant<
std::unique_ptr<char>,
std::unique_ptr<short>,
std::unique_ptr<int>,
std::unique_ptr<unsigned long>
>;
int main() {
auto md = std::unique_ptr<int>(new int(123));
Mixed mixed = std::move(md);
std::cout << *boost::get< std::unique_ptr<int> >(mixed) << std::endl;
return 0;
}
unique_ptr是仅移动的,可以在变体中使用。上面的例子可以编译和工作(C ++ 11)。