我目前正在编写一个需要操纵树结构(抽象语法树)的程序。在树中,节点将其子节点作为unique_ptr拥有,如下所示:
struct Node {
// to replace node itself in the tree:
// points to unique_ptr that owns this node
// a node can be stored in different unique_ptr types
// -> for example: NodeY could be stored in unique_ptr<NodeY> or unique_ptr<NodeX>)
// -> thus self has to be of type unique_ptr<Node>*
unique_ptr<Node> *self;
// ...
};
struct NodeX: Node {
unique_ptr<Node> child1;
unique_ptr<NodeY> childY;
};
struct NodeY: Node {
unique_ptr<NodeX> child1;
unique_ptr<NodeY> child2;
vector<unique_ptr<NodeY>> otherChildren;
};
struct NodeZ: NodeY {
// ...
};
// and a lot of other nodes with different child types ...
在更改树时,应该可以替换树中的节点。为此,我在每个节点中存储一个指向拥有的unique_ptr的self
指针。替换操作如下所示:
// could replace node:
void visitNodeY(NodeY *node) {
if (node->someCondition) {
// replace
auto newNode = make_unique<NodeZ>();
unique_ptr<Node> *self = node->self;
// replace with make_unique<NodeA>() would break inheritance hierarchy, but i will not do it :)
*self = move(newNode); // replace and delete old node
node = self.get(); // get new address
node->self = self; // self still points to same address, only contend of unique_ptr has changed
}
}
现在的问题是在构造节点之后设置self
指针。为了实现这一点,我正在使用reinterpret_cast
:
void createNodeX_children(NodeX *nodex) {
// create childY
nodex->childY = make_unique<NodeY>();
// ...
// is that save?
nodex->childY->self = reinterpret_cast<unique_ptr<Node>*>(&nodex->childY);
}
我的问题现在是:只要我不破坏上面提到的继承层次结构,是否可以通过这种方式使用reinterpret_cast保存?
不要reinterpret_cast
。您可以使用std::unique_ptr
的constructors多态转让所有权。